I have noticed that ever since Joe Biden took office, he has tweeted from @POTUS. However Donald Trump, for example, tweeted primarily from his personal account, which is suspended. When @JoeBiden tweets, it is solely retweets, mostly of @POTUS content. Kamala Harris seems to have made a similar move as well.
Is there any official or plausible reasoning for Joe Biden not tweeting directly from his personal account?
@POTUS, according to Twitter (https://www.wsj.com/articles/twitter-says-it-is-permanently-suspending-account-of-president-trump-11610148903), is the 'official' account for the Office of the President of the United States. It is a de facto arm of the executive branch in the same way that any other public-communications aspect of the office would be. (Theoretically) When it is used, it carries the weight and authority of the Office - it is, essentially, official communication.
@JoeBiden is the account of Joseph R. Biden, a private citizen. Communication therefrom does not carry the official nature in the same way, and so to use it is ethically incorrect, if not actually illegal in any way.
The word 'republic' derives from Latin (res publica) to mean "The People's stuff." Meaning the President is acting as a trustee, responsible to the People and charged with taking care of their stuff. If the person of President and the Office of President were the same, it would be the President's stuff, not the People's stuff. It's super abstract to be sure, but it's a quintessential feature of what it means to have a republic. This was a choice made by the framers in reaction to a system where everything was understood to be owned by the monarch, divvied up among people delegated to work that land since the King couldn't do the job himself.
No firewall between trustee and beneficiary/grantor is needed under a monarchy, because they're all the same person. In a republic, however, the public are the grantor and beneficiary, and the official is the trustee - but they are also a beneficiary and grantor in part. This introduces an unavoidable conflict of interest - one that is worked around by keeping a procedural firewall between the acts of the trustee as President, and their acts as a private citizen.
Donald Trump's style as President featured a broad disregard for norms of conduct, for which he was both broadly criticized and hailed. It was entirely within his style to use his personal brand and communication channels, because he viewed himself as 'The President' instead of simply the person who was occupying the Office of the President. This is also why he got into fights with members of the White House Counsel, often claiming that they should be acting differently: He wanted them to behave as if he were their client, when in normative actuality it's the Office of the President that is their client. (There's also a string of West Wing episodes about this nuance.)
A big part of Biden's platform and entire political character revolves around re-upping political norms and restoring the traditional relationships of political institutions. To that end, using his own, private Twitter handle to broadcast official messages would be in contravention of his demonstrated beliefs and values. In fact, using it much at all while he occupies the Office could create the appearance thereof, thus why he's mostly only using it for retweets.
By only tweeting official things from @POTUS, Biden isn't making @JoeBiden a public forum.
A circuit court ruled that Donald Trump's use of his personal Twitter account for public statements meant that blocking people on it contravened their First Amendment rights.
It is incorrect to say it is unethical to use a private @joebiden account. Indeed the opposite is true. @POTUS is an official US government account and can only be used for official government business. It cannot be used for partisan political reasons for example. So it cannot be used to endorse Democratic party candidates for example. It would also be incorrect to tweet about what he had for breakfast or his favorite baseball team. Consider it an account to be used only for official issues.
@JoeBiden is a personal account and not subject to any US government rules or restrictions. Therefore it can be used for any reason whether it is endorsing candidates, his favorite movies or anything else such as your own personal account. Someone can talk about work items on a personal account but they should not discuss personal issues on a work account.
The issue of whether a President can block people on his personal account is unresolved. The Appeal Court ruled that Trump's personal account could not block critics because it was a public forum. However the Supreme Court dismissed the case on appeal as moot as Twitter blocked him from accessing the account and he was no longer President. There is no current precedent whether the @JoeBiden account would face court rulings declaring it a public forum the way @realdonaldtrump was.
Donald Trump and his supporters argue that public officials that use their private accounts instead of their official government accounts should be sent to prison. They even have a slogan for it: "Lock her up!"
President Biden ran on a platform of unity and reconciliation, so doing the exact thing that Donald Trump and his supporters claim is illegal, would undermine those efforts. It doesn't make sense to risk dividing the country over something as silly as which Twitter account to use, so the easiest solution is to just do what Donald Trump and his supporters want: that the President of the United States of America uses the Twitter account of the President of the United States of America.
@RealDonaldTrump instead of @POTUS throughout his presidency and millions of people followed that account. If Trump really thought that the president of the United States shouldn't use a private twitter account, why didn't he lead by example? (the way Barack Obama did, by the way, when he created the @POTUS account)