They're really not. There's so many factors going into it that people ignore just because the on-paper specs say something, it's crazy. It's ambient light, it's the paint your walls have, it's what you focus on when looking at the TV, and on and on.
https://www.nature.com/articles/lsa2017168
Besides the physical differences, another big thing people don't consider is how poor the source itself is. Meaning, it doesn't matter how black your TV can get when the content you're watching is poorly mastered. For games in particular you'll find, if you have an oled, that blacks levels are raised considerably and you aren't going to see an actual deep black. In fact, if you also calibrate your display you'll see how poor some of the reference material is, where it's not properly mastered for either SDR or HDR. Not especially surprising, if you see how these games are made and on what hardware, but it's something to consider. Audio people went through the same struggles, where they find out after getting new equipment and properly calibrating it that their favourite records didn't sound better but rather worse, due to how they were mastered (and whom for).
Remember the down-grade struggles, when PC ppl complain consoles keep games back due to their limited power? Kinda same here. The content wants to reach the most people, and most people have crap setups, so guess how that consideration plays into it.
