IIRC, Kirby Collection was charging $300/space, but that might be for below-grade construction. An above-grade structure probably needs to charge about $200-250 to be cost-neutral with the residential square footage, which is 10-15% of the rent of a typical 1BR in the area. Though since the actual requirement in Houston is 1.33 spaces per 1BR unit, people are probably paying 13-20% of their rent to store their cars.
Then we need to take a drive up to Gallery Furniture. Its the biggest competitor in town regarding furniture stores. Look around nothing, but other furniture competitors and they probably drop like flies every now and then, yet that area consistently has the highest concentration of furniture stores in the entire city. If either of the grocery stores do fail and die then fine, but the fact that the competition took place means that more are going to want to join the competition. To use your sports hyperbole, do those NBA teams play one game and if they fail the competition then they don't play another game all season? No. They play like 80 more games? Do they play one season? No they play many more seasons. They will keep playing because one game isn't enough to settle the score for good and the audience wants more games which means the supply isn't going to end. Its certainly possible for a city to handle 7 NBA teams if the supply for basketball is that ridiculous. Even your hyperbole still doesn't work because we have cities with 2 major competing sports franchises! Typically NYC and LA and there are many cities around the world which support multiple soccer franchises/clubs. Supply and Demand plus Competition is one of the few things in our reality that consistently scales both small and big. In only very few instances (and most times by decree or by force) is there a monopoly or an instance with only 1 entity exist without competition.