IBM made the PC but others monetized it, most notably Microsoft followed by Compaq and Dell. [0] The PC architecture was not proprietary, and IBM didn't control the operating system.

By contrast IBM made boatloads of money off mainframes and their advantage was durable. That business line is still quite profitable even today. (Just not very big in comparison to the IT market.)

[0] https://www.forbes.com/sites/timbajarin/2021/08/25/attack-of...