It's a really personal thing tbh. When I first started bottoming, I think the excitement of something new helped maintain my erections, plus having come from a traditional 'straight' sexual background, it had always been based solely on my penis as the source of pleasure. As I bottomed more, I got more in-tune with the different sensations of anal, and when you focus on it, it's actually pretty intense.
I found then that the more I focussed on the anal stimulation, the less important/the less need I felt to touch my penis. I'd always be erect during foreplay, and at the point of penetration, but soon after, I'd go to more of a semi and would only get fully erect again if I touched my penis/masturbated.
We're years into my life as a near total bottom now and whilst I get hard for oral and foreplay, I'm now totally soft during sex - it's not that I don't enjoy it - It's the most incredible feeling in the world having a penis inside me. I just don't need to be erect to enjoy it. It took my bf a while to understand - he thought I wasn't enjoying it, despite my moans, my precum, and my eventual ejaculation. He'd only topped guy who'd stayed hard the whole time before. Literally, i'll be rock hard during foreplay, but as soon as he starts touching my hole, i'm completely soft within minutes - usually before he's penetrated me - and then I'm soft for the duration.
Do I miss erections during sex? Not really - they get in the way and they distract me from the anal pleasure.