Why didn't the C64 come with Simons' BASIC in the box from 1983 onward?
And maybe they could have even given the cartridge for free to people who have already bought a C64 without it.
Wasn't it because Jack Tramiel was too cheap and just wanted to make use of his existing MS BASIC licence?
Because they believed only a small fraction of customers would care a lot about a better Basic interpreter, whereas the vast majority would care about price. As for giving things away for free, Commodore was already engaged in a cutthroat price war with Texas Instruments that almost sank the company. They could not afford to give anything else away for free.