They delayed refreshing the X and S for a long time, I believe, in part because these two models are low-volume and therefore don't warrant a high allocation of battery supply and manufacturing floor space. Why refresh them now, then? I think they are using the 2021 refresh of X and S as a spur for the 4680 battery ramp (see conjecture that Plaid+ is going to be 4680).

Adding more models and variations doesn't do them much good when their demand for the mainstream 3 and Y far outstrips their battery supply, both today and into the near future, even with them ramping battery supply as hard as possible.

Brands that are making a wide range of electric vehicles are taking a significantly different approach. But seeing as they too will be constrained by a small supply of batteries, I am not sure the diversity will be as valuable on their bottom line.