He spent a decade of nights-and-weekends effort on making kids better at math and science, taking what I understand to be startup level risks in the beginning. How much do you think he should make? Mr. Rogers was paid more than $800k/year if you adjust for inflation[1][2].
If he thinks other people should donate a whole bunch of money, shouldn't he donate a whole bunch of money if he has it? Maybe he already does this, I don't know. If he took a lower salary he would effectively be doing this -- in a publicly verifiable way. It's a matter of "skin in the game".