I don’t think the reason we can’t get good UI/UX out of Matrix or other FOSS chat services has much to do with budgeting concerns. Consider that other FOSS services have a good selection of frontends that people actually like. Example: fedi
Whether you prefer Soapbox, PleromaFE, Misskey, or even Mastodong, the point is, these aren’t UIs that people merely tolerate. They’re UIs people actively like. And they were made by “some guy” on a gratis basis.