Some people don't need the rear seats in their car, so they should cost extra...Some people need a Toyota Camry. Some need a Toyota Supra. Apple sells both, pro branding aside.
This is a production thing and not a marketing thing. Chips dont always come out perfect, so you need to bin them for what class they fall under, if you have a m3 chip that can operate just fine with 8gb of ram and 256gb of storage, why throw it out?
Except its been shown that "DIY" RAM and SSD upgrades on an 8/256 M1 system are possible and work fine - just too complex and risky to be a practical proposition:

M1 Mac RAM and SSD Upgrades Found to Be Possible After Purchase
Technicians in China have reportedly succeeded in upgrading the memory and storage of the M1 chip, suggesting that Apple's integrated custom...

Anyway, Apple was shipping paltry 8GB RAM systems even when (a) they were using Intel chips and (b) you could upgrade them with 3rd party RAM and they'd work perfectly.
Sorry - this is pure marketing. The upgrade charges have nothing to do with - and are completely disproportionate to - actual costs.
Apple have never been cheap, but the real problem is that the base spec for Macs has been stuck at 8/256 for ten years - and the upgrade prices have remained much the same too. The issue is not new, but its getting more and more ridiculous as prices (particularly for large SSDs) have dropped and the amount of storage and RAM used by higher-resolution images/video and script-laden web pages has increased. It was already getting bad before Apple Silicon.