Because companies are not some monolith, all doing identical things forever. If someone sees a new angle to make money, they'll start doing it.

Data General and Unisys did not create PCs - small disrupters did that. These startups were happy to sell eggs.

They didn't create them, but PC startups like Apple and Commodore only made inroads into the home -- a relatively narrow market compared to business. It took IBM to legitimize PCs as business tools.