It's called, “getting your VR legs”, akin to sea legs. It worked for me, at least. As an extreme example, I can now play as a character in a space suit, twirling and spinning around for hours, without getting motion sickness. I also regularly play rally racing games where I'm constantly subjected to bumps and jumps, and don't notice it at all. This was after around 100 hours of VR, I think.

Actually I've found the experience somewhat magical, in that I get the same stress relief from being couped up all day by leaving the house to go do something outside as just playing a game for an hour or two. It feels like I'm actually going to another place, nowadays.

This really only started when I got the high end, Valve Index, which has a 90hz+ refresh rate, so maybe that has something to do with it.