I guess it wasn’t coerced

It was coerced in the sense that the biggest party donors had refused to put any more money into his campaign. Biden fundraising after the debate absolutely tanked. That's one reason why Harris got crazy post-dropout fundraising numbers. She caught a windfall of money that had been earmarked for Biden.

Did anyone have a gun to his head? Probably not. But they might as well have. You can't run a national campaign full of high dollar media markets without billions in donor dollars.