Does a bottom need to stay hard to please a man's cock? And for getting fucked to feel damn good? Nope and hell nope.
A bottom doesn't even need to be hard to squirt some cum out and have an orgasm. Or five. As someone who has anal sex 14 times a day minimum (15 times receiving, and -1 giving for a total of 14) I can tell you some guys want to see their bottom with a boner as it's a sign of pleasure.
But really, hard on or not, all the nerves are still there in both your cocks, in and around that hole, and the rest of your body. The penetration is still happening. The bill at Chipotle has already been picked up. What, don't you all put out for a burrito? With guacamole?! And mild sauce? In a red basket? Weird.
Maybe you love each other so it's also about just being close, that connection, figurative openness, becoming one, holding each other tight. Or maybe you're with the dommiest dom guy who ever dommed (and I'm not talking about that alleged sissy bottom Dom DeLuise). Your dom guy actually doesn't give a fuck about your pleasure, except in that he knows your actual pleasure is to make him happy. He'll want your hands on him, not on your cock. Doms are swell, aren't they? All three of them in the United States.
Physical and mental arousal are curving, non-linear, unpredictable beasts. Ride the wave. Erection or not, you're fucking. And that's amazing. Because I say it is.