Speculating, but I'd wager it's to clear out existing inventory by phasing out the old chips on other SKUs over time. E.g., you start with the expensive Macbook Pro models when you have fewer M3 chips in production, since those will sell slowly, and then you clear out your remaining M2 inventory in the Air lines while waiting for a "refresh" when M3 production is more ramped up.

I have no idea what Apple's sales are for the macbooks or if Airs sell more than Pros, etc., but they're definitely making profit this way to be this consistent in their approach.