Your post is proof that I spend too much time rolling with white belts.
No but seriously, contrary to what people preach every time I roll their is a winner and a loser.
Actually, more like success and failure. That success and failure really has little to do with tapping. If I can't sink an armbar from mount on a white belt or if I get held in side control for one minute by a blue belt, that crushes my spirit a lot more than getting randomly tapped for some reason. So in my head I truly lose all the time. But in terms of people getting submitted I've seen it pretty balanced.
Again partly because the ranks are lopsided where I train, and partly because I think upperbelts start cherry picking their matches after a while.
You've been a purple for quite a while, right? So it would make sense to me that you rarely get tapped by a lower rank because that's only white/blue. And it's going to take a pretty beastly blue to beat a guy who has been training 10-15 years now like you have.
I'm a brown belt. Getting tapped by a white belt would be pretty strange, like once a year kind of thing. That holds for even the "yeah but he wrestled/did Judo/trained no gi for years" kind of white belts.
Getting tapped by a blue belt really depends on the blue belt. Most will not. Maybe 2-3 can do so occasionally. One guy beats me consistently. He was a high level competitor, but he is backing down some now since mat skills don't pay the bills.
Once it gets up to purple belt, it's not really weird at all for me to get beaten. Purple/brown/black all beat each other back and forth all the time at my gym. The only two really above that fray are two black belts that train full time and have competed at a high level. Other than that, pretty much any of us can beat another one and it's not notable at all.
Nobody cherry picks at our school luckily. If I am selective, it's towards the harder guys if anything. I know the handful of guys that are around my size that can give me challenging rolls -- a couple blue belts, a decent amount of purples, a handful of browns, and one or two blacks. So I just pick my partners based on membership in that group rather than any kind of belt ranking. I will usually beat the black belt I train with the most, and I will usually lose to the blue belt I train with the most. That's okay with me. They're both tough rolls for me where I learn a lot, so I gravitate to those guys.