why do some online casinos offer way higher RTPs than competitors.

I've been browsing around for new blackjack and roulette options and noticed some online casinos pushing games with RTPs that are way higher than others. I saw blackjack tables listed at like 99.8% and even some slots advertised over 98% RTP. Then you go to other sites and see the usual numbers much lower or the standard house edge. Are these higher RTPs for real or is there usually some catch involved? Feels like there's always a trade-off when something looks too good.

Is it just a marketing thing, or are they trying to pull in more players by taking smaller profits short-term? Also, for the folks who chase high RTP, do you ever actually see the difference when you stick to the long-term, or does variance make it impossible to tell? I'm trying to stay disciplined but sometimes these numbers make me second guess my usual spots. Anyone got firsthand experience with these higher advertised RTP casinos?