Founders go on Bills, not Presidents
The people on US currency aren't there because they were presidents - they're there because they founded the country or prevented its dissolution.
It so happens that some of the people on our currency are presidents, but the actual qualification is that you either founded the country, or were instrumental in preventing its dissolution.
Franklin and Hamilton were not Presidents. They were founders. Washington was a president, but he was also a founder. Lincoln and Grant were also presidents, but they were known for keeping the country together when the south decided it would rather leave than give up slavery. And then Jefferson on the 2-dollar bill was also a President, but he's on the bill because he was a founding father.
There's also Kennedy on the half dollar and Roosevelt on the dime. FDR had polio which paralyzed him and there was this whole campaign to send him dimes.
In fact, all principal founding fathers are on currencies except John Jay, James Madison, and John Adams.
It's funny that Johnson, who was president between Lincoln (16) and Grant (18), never gets any attention. He was a VP who assumed office after Lincoln was assassinated, but he was still a President for 4 years! Kind of mean.