The reason is largely historical, the office of President was first introduced in the Weimar Republic of Germany, with significant political powers according to its constitution.
Article 25 of the Weimar Constitution the President had the power to unilaterally dissolve the Reichstag
Article 48 of the Weimar Constitution the President had the power to unilaterally suspend civil liberties.
Article 53 of the Weimar Constitution the President had the power to unilaterally appoint and dismiss the Chancellor and the cabinet.
Basically this created a very unstable sort of government and the Reichstag was constantly getting dismissed and re-elected. Indeed there were 8 elections between 1919 and 1932. Also the cabinet of the Weimar government kept getting appointed and dismissed as the President would appoint them, but they didn't enjoy support in the Reichstag who would promptly dismiss them. This led to the President Hindenburg appointing a bunch of cabinets who outright didn't enjoy support in the Reichstag and were referred to as "presidential" cabinets.
However it all changed in 1933 when Adolf Hitler rose to power, to some degree through abusing powers invested in the office of the President such as with the Reichstag Fire Decree. I quote a translated copy of the text below:
On the basis of Article 48 (Weimar Constitution) paragraph 2 of the Constitution of the German Reich, the following is ordered in defense against Communist state-endangering acts of violence:
Articles 114, 115, 117, 118, 123, 124 and 153 of the Constitution of the German Reich are suspended until further notice. It is therefore permissible to restrict the rights of personal freedom habeas corpus, freedom of (opinion) expression, including the freedom of the press, the freedom to organize and assemble, the privacy of postal, telegraphic and telephonic communications. Warrants for House searches, orders for confiscations as well as restrictions on property, are also permissible beyond the legal limits otherwise prescribed.
As you can see this was clearly an abuse of the power of the president and it along with the Enabling Act led to the downfall of democracy in Germany and the rise of Hitler as chancellor. In 1934 Hitler combined the offices of President and Chancellor to become the Fuhrer
So in 1949 when the West German Basic Law (or constitution) was written, the authors intentionally reduced the powers of the president and made him indirectly elected i.e elected by the Federal Convention (which basically consists of the entirety of the Bundestag and some other regional leaders) instead of the public. Now some dude who is indirectly voted in by the parliament isn't going to garner international headlines unless he is particularly controversial, since in a democracy he isn't that powerful. Also because the public don't need to go to a polling booth to tick his name they simply don't know or don't care.
Nowadays the de facto powers largely lie in the fact that the President of Germany has considerable leeway in exercising his duties, which are quoted as follows:
- Proposing the Chancellor to the Bundestag.
- Appointing and dismissing the Chancellor and Federal Ministers
- Dissolving the Bundestag under certain circumstances
- Convening the Bundestag according to article 39 of the constitution
- Signing and promulgating laws
- Appointing and dismissing federal judges, federal civil servants, and commissioned and non-commissioned officers of the Armed Forces
- Exercising the power to pardon individual offenders on behalf of the Federation
- Awarding honors on behalf of the Federation
- Representing Germany at home and abroad
For example he could independently make representations and political suggestions which would not be allowed to some other heads of state whose role is more ceremonial e.g Her Majesty the Queen.
The President of Germany also possesses some reserve powers if all goes to pot as outlined by Article 81 of Basic Law
If, in the circumstances described in Article 68, the Bundestag is not dissolved, the Federal President, at the request of the Federal Government and with the consent of the Bundesrat, may declare a state of legislative emergency with respect to a bill, if the Bundestag rejects the bill although the Federal Government has declared it to be urgent. The same shall apply if a bill has been rejected although the Federal Chancellor had combined it with a motion under Article 68.
If, after a state of legislative emergency has been declared, the Bundestag again rejects the bill or adopts it in a version the Federal Government declares unacceptable, the bill shall be deemed to have become law to the extent that it receives the consent of the Bundesrat. The same shall apply if the Bundestag does not pass the bill within four weeks after it is reintroduced.
During the term of office of a Federal Chancellor, any other bill rejected by the Bundestag may become law in accordance with paragraphs (1) and (2) of this Article within a period of six months after the first declaration of a state of legislative emergency. After the expiration of this period, no further declaration of a state of legislative emergency may be made during the term of office of the same Federal Chancellor.
This Basic Law may neither be amended nor abrogated nor suspended in whole or in part by a law enacted pursuant to paragraph (2) of this Article.
President is basically ceremonial, but has some leeway in exercise of duties. You haven't heard of him because the public don't elect him and his powers were cut because Hitler used them to become a dictator.