And of course, no closed software has _ever_ had a poor UI/UX.
Bad UX is subjective. Money doesn't change that.
Suppose we want to optimize user productivity. For any given UX, some users will feel they're more productive with it, and some less. Finding a UX that maximizes the number of users who feel productive is going to help attract users to the product, and money can buy the design expertise needed to find that UX.
It might be the case that users only feel more productive with a given UX and aren't actually more productive with it. Even then, if a majority of potential users think that the UX is making it easier to accomplish their goals, a project will have an easier time attracting users.