Well, first of all, the internet isnt secure, and thus voting cannot be ensured valid. It would be corrupted by foreign and domestic interests. Sites can be hacked, identities can be stolen. In order to ensure that every citizen - and only citizens - vote, its best to protect the system with in-person, signed, and ID-enforced voting booths.
Two, you cant ensure that everyone has access to the internet. Or that those who do will have during the open polls. And what does it mean for the future of our country if the internet goes down for whatever reason (EMP, for example, we wouldnt even have the infrastructure to revert)
Three, we require representation for a multitude of reasons. The most practical of which is that we cant call on the People to vote every time a minor decision comes up... and we surely cant wait on the People when an emergency comes up. And who has the power to enforce the outcomes of a democratic decision anyway, when there is no centralized power? How do we hold civil public debates about policy when every one of the 700 million citizens are equally welcome and equally qualified to voice their opinion? But there is the obvious other reason few talk about, which is simply that direct pure democracies are a horrible idea, with horrible, evil outcomes. Two wolves and a sheep voting on whats for dinner... it doesnt matter that it's democratic; that doesnt make it "good". The sheep still has rights to be protected and defended. The shepherd is the representative that steps in and says to the majority 'no!, the People are crossing the line'. Representation is about protecting the minority FROM the majority, under Constitutionalism.
On a side note, I fear that any military leader or bureaucrat, etc., who answers solely to the democratic People rather than to a singular elected official could easily commit a coup... I cant imagine any individual citizen or group stepping up to the plate to fight such a thing the way elected leaders with the responsibility of their office would. A vague mass of "the People" cannot be at the top of government operation. In our government the elected officials answer to the People, yes, but military and bureaucrats are beneath them rather than immediately beneath the People. There would simply be too little direct accountability. There is no consolidated power of the People except through their leaders, and should those leaders not give up power there is little the People can do. Thats why a tapered pyramid of power is vital, with officials accountable to those above them, and those at the top (not a single individual) to the people.
Fourth, representatives who make decisions are usually pretty informed. They hold hearings, read reports, get the statistics, listen to experts, and for better or worse, assuming they arent malicious or corrupt, will make the best possible decision. Do you honestly trust the People of your nation to be able to vote the same way? Can you trust them not to vote purely by emotion, especially when social and mainstream media paints false narratives and fails to report honest facts? Do you trust your fellow citizen to do and comprehend the research? When individuals are in a group there is something called the diffusion of responsibility, as well as peer pressure, and the frequently incorrect "wisdom of the crowd".
On a side note again, some of the information our politicians are privy to are of a confidential matter. National security. Do you trust all 700 million citizens with this information? To keep secrets, and wont be bought out by foreign enemies, compromising the lives and citizens and military and the freedoms we all enjoy?
That said, I do appreciate the idea of putting ones ballots online so that the voter can verify that his or her vote was counted, and counted correctly. Though Id be wary of breaching peoples anonymity and having neighbors and employers "punish" people for voting "wrong". Anonymity is important, but being able to verify your own ballot and that no "extra ballots" are associated with your residence when they shouldnt be. We dont need dead people and pets voting democrat. I do believe that every citizen registered to vote should negotiate with the registrar a location to vote, and not have "options" come voting day, where they can drive around and have their vote counted more than once. Everyone should have a designated booth where their one and only cast is anticipated.
I understand that the democrat left would push for something like this... but if you are against foreign interference, corruption, voter fraud, and you want to protect minority groups (regardless of race or religion) from oppressive majorities (regardless of race or religion), and you honestly believe that some demographics lack the privilege of internet access, if you dont want to be responsible for decisions that could cost lives, and dont trust the general public to cast the most informed votes, then you kind of have to go the other way on this...