Why is John Hanson not taught in us history?

they do not teach us about John Hanson because in the constitution they want us to believe that George Washington was the first president

... because George Washington was indeed the first President of the United States.

John Hanson was the first "President of Congress" (sometimes called "President of the United States in Congress Assembled") under the rules set by the Articles of Confederation. The President of Congress was a ceremonial position, dating back to the first Continental Congress before the Revolutionary War even began, which was vaguely similar to the current Speaker of the House- but with almost no power whatsoever. It was an apolitical, impartial moderator position, whose primary function was to ensure that rules were followed; he was not allowed to participate in the debates, nor did he have any executive power whatsoever. He couldn't even sign documents unless Congress ordered him to!

It was a completely separate and unrelated position from President of the US, and ceased to exist when the last one resigned in 1788 (almost six months before Washington became the first POTUS). With the ratification of the US Constitution, the position was no longer necessary, as Congress was split into the House and Senate, with their own rules and officers. The Constitution also set up the President of the US as the supreme executive authority, and largely separated him from Congress.

We generally don't hear about John Hanson in school because he was one of many Presidents of Congress (he was neither the first nor the last- he was simply the first under the Articles of Confederation), and the Presidents were generally not all that important. Because the Continental Congress did not like the idea of giving one person a lot of power, they intentionally gave the President of Congress almost no power whatsoever, instead preferring to delegate authority to committees.

The only similarity between the President of Congress and the President of the United States is the title "President". Otherwise, they have virtually nothing in common.