"Some people can do it" is not an argument that "everyone can do it".

I'm willing to be convinced by an actual scientific reference, but at this point consider your position to be a line of BS.

Many people in western cultures who use chairs all the time are very flexible.

There is a general belief in the meditation community that people of European ancestry have some mobility differences - for example lotus position is a rather advanced posture in the west, not a taken for granted comfortable sitting position.

People use chairs in Asia.

When people do yoga, some people become very flexible and others don't. It isn't considered a big deal in most forms of yoga. Likewise Asian Buddhists generally don't stress out over whether western Buddhists can sit in lotus position.

If not trying to do a full depth squat for athletic purposes, so-called "lack of mobility" in that exercise has little or no association with health or survival deficiencies. Thus, it is likely that no particular mobility has been selected for, and a range of genetic capacities exists in the population.

Personal trainers, "phys ed" teachers, and others like to make up arbitrary "minimum acceptable standards that they actually know in advance some otherwise normal people will fail to meet.

That way people can bullied into paying for useless routines instead of just doing the exercises that work for them, someone can fail phys ed so that the teacher isn't accused of passing everyone, etc. Also, the use of arbitrarily defined standards that "everyone" "must" meet is very good for steroid sales.

Olympic weight lifting is like ballet - it looks cool and requires a lot of training to be good at it, but many people simply aren't genetically flexible enough to do it at all.