My girlfriend and I had always done some anal. Maybe a third of the time we had sex involved anal. But we still enjoyed vaginal sex because that's what we'd grown up thinking as 'normal' sex. (Seems a weird thing to say now)
Then a bit over a year ago we came across the concept of anal-only on the internet and we spoke about it for a while. We decided we were going to try to do a year of anal only. We adjusted to it pretty quickly. We'd have sex about 3-4 times a week and always anal. It was really good. We definitely got better at it throughout the year. Quicker, less warmup needed. And she started having anal orgasms, which she'd never had before.
So a few weeks ago we finish our year of anal-only and we try to have vaginal sex again. We were in the middle of it, our first vaginal sex for a year, and it just wasn't feeling very good for me. It wasn't stimulating me in the way I liked. And I soon found out my girlfriend felt the same way. She said "This isn't very good, is it?". "No, not really" I replied. She smiled at me and asked "Do you want to stick it in my butt?". Hell yeah I did!
Suffice to say, we've gone back to being anal only now

Sorry for my english. Not my first language. Hope you can understand what I mean.