why isn't anyone calling for Trump to drop out.

Most of the people who think Trump should drop out have been loudly opposing him for a long time. There isn't just one single thing they object to, no great unifying theme they can point at and say "This is why he should not run," because Everything about him is a reason why he should absolutely not be president. Even his Felony conviction is, while perhaps more than a drop, just a splash in the bucket of what should be utterly career ending circumstances.

The people who still support Trump don't care about any of that. They're not going to suddenly see one particular turn-off and decide that's it, that's why Trump should back out. They're committed, in too deep, they can't back down now because it would mean the Libs were actually right all along, and that presents, to them, an existential threat. And in the end, it's the Republican way.

When Democrats, even popular ones, fuck up, other Democrats are much more likely to turn on them, to call for and get resignations. With Republicans, that's almost unheard of. Republicans take Part Unity to an extreme, circling the wagons and assuming a full defensive position no matter how incredibly abhorrent the crime, no matter how blatant the evidence. Today we're seeing the perfect example. Biden fucked up a debate, stumbling over his own words like an old man well past his prime, and the party is calling for him to step down. Trump has built his whole political career on stumbling over his own words, with the only cogent statements he manages being blatant lies, and his people would rather murder their neighbors than see him lose.