To make upgrades incredibly expensive, allowing them to have the same product generate revenue as both an expensive mid-range machine as well as a ridiculously expensive "professional" machine. Why make different products when you can sell the same product at different prices?
In case of intel macs, the soldered RAM should have made the device and RAM options even cheaper, as the BOM is simpler. The only real argument against soldered RAM was DDR5 in SODIMM being bad - which LPCAMM2 fixes.
If they didn't use it specifically to price gouge, the soldered RAM wouldn't have been a problem. 64GB of RAM costs practically nothing at market prices, so they could honestly have had a single SKU with max RAM without notable price change over entry level - heck, maybe the BOM reduction would even sponsor it.
... But then they'd lose their mechanism to drain companies with deep pockets for necessary upgrades. Being sensible and fair is not profitable.
