Regardless of whether or not the cab companies are monopolies or are small mom-and-pop shops, they provide a vastly inferior experience to Uber/Lyft/etc., whether due to availability at peak times, or just the general experience of hailing, payment, etc. That's why people are rooting for the new alternatives.

Whether or not Uber is "more" of a monopoly in some regions than the incumbent(s) is irrelevant.