Lots of software has monopolistic tendencies and/or large switching costs. Most customers (outside of developers) don't have the ability to reliably ascertain

Lots of software has monopolistic tendencies and/or large switching costs. Most customers (outside of developers) don't have the ability to reliably ascertain the true quality of software, at least not before buying it (as they aren't software experts). And (especially for the worst software, aka "enterprise") the people buying it are not the people who will actually use the software, so there is little incentive to improve the UX of it beyond the bare minimum. And fundamentally... businesses don't compete on quality. They compete on profit.