According to Elon during the Q4 2021 call, they are CHIP constrained in 2022, but not CELL constrained, and not 4680 constrained. Of course the reason they don't feel 4680 constrained may be because they are not immediately switching all MY car production to 4680 cells. On the other hand, they also need to use their 2170 supply somewhere.
Personally, I think that MOST new to Tesla customers who order a MY either don't care, or don't even know, that their car may have 2170's or 4680s. It is only the well informed fringe buyer, such as myself and other forum readers, who sometimes cares about such internals. Tesla probably wants to keep it that way.
Thus I think Tesla is looking at the logistic COSTS of shipping cars, and shipping cells, and telling themselves it doesn't make economic sense to boost their shipping costs. Given their current delivery times, they we won't lose many orders by not rushing the cut over to 4680s everywhere at once. So rushing would just guarantee incurring additional costs, but would not guarantee generating additional profit.
I also suspect that Tesla is intentionally using the Austin factory where Elon has his eyes on things to iron out the structural battery pack production ramp bumps in Austin, then planning to share the knowledge with the other factories. Instead of having all the factories trip over the same issues.
If they are cautious, they also want to see what happens when they have 10's and 100's of thousands of cars in customer hands. Sure they have done in-house testing, but ultimately you never know how good a product you have until lots of customers use and abuse it. They saw what happened with the Chevy Bolt, and don't want to risk anything remotely like that happening to ALL their 2022 MY production.