They probably didn’t make much on the software locked car, so they are banking on people that buy it to pay for the upgrades. They also didn’t want to invest in a new assembly like just to produce this limited run vehicle

If I remember correctly, rear heated seats were only extra (and pre-installed just needing a software update to enable) once. There was a time when the cheapest model 3 was slightly too expensive for some rebates, so they sold a software locked version that was just barely was under the limit for the rebate. To reduce the initial price they software locked the rear heated seats, along with some battery capacity, and maybe one or two other things, all of which you could pay to unlock afterwards.