Tyres are designed for suspension. They were the only suspension for many years.
The problem for flex else where is that tyres give alot of suspension (if you thinky about travel to hitting the rim we are talking a couple of inches). So even a soft tail is adding a huge amount travel
The other problem is that suspension bikes are good at being suspension bikes. Its not like in the early days when the choice was rigid or flexy bobbing horror. Now you can but a suspension bike all the way from like a hard tail with a bit more comfort to Downhill bikes
The clever thing about pivots is that one way they bend the other way they don’t. This is a much harder trick for a frame, wheel or fork. I can remember project 2 forks coming in with straight blades to improove handling through reduced flex and I can remember the improvement
There may be a rigid neach with more Jeff Jones like stuff. But the main stream will be rigid rigid or proper FS
But I could of course be wrong