Local government doesn't allow competition against the big company they have some form of agreement with.
Big company buys them out to shut them down so they don't have to compete with it.
Big company crushes them via pricing reduction (until competition is gone so it goes back up), sicks the lawyers on them (doesn't matter if valid or not, defending oneself in court is expensive), or a highly expensive negative PR campaign.
It all depends on the state, county, and/or city. What can work in one area might not be feasible or legal in other areas. It's a huge multi-headed issue in the US.
Disclaimer: I used to work at a wireless ISP and I am going to decorate your comment.
Oddly, local government has no say over it. As long as you can legally place antennas and/or dishes in the right spots, you can do whatever you like. You can run on crappy 2.4GHz or 5GHz radios or use more fancy FCC leased spectrum 30GHz-60GHz radios or even line-of-sight optical lasers. You will typically run a 20Mbps to 1Gbps connection to an apartment/condo complex then feed individual units from there (i.e. each customer isn't getting their own wireless connection unless you are a fancy business paying for that level of service).
Big companies don't care much about tiny ISPs here and there. What's more likely is the biggest of the tiny ISPs will buy you to goose their numbers.
If your tiny ISP is aggressive in servicing buildings, you may see Comcast running counter promotions against your pricing. Welcome to the free market.
Local government doesn't allow competition against the big company they have some form of agreement with.
Big company buys them out to shut them down so they don't have to compete with it.
Big company crushes them via pricing reduction (until competition is gone so it goes back up), sicks the lawyers on them (doesn't matter if valid or not, defending oneself in court is expensive), or a highly expensive negative PR campaign.
It all depends on the state, county, and/or city. What can work in one area might not be feasible or legal in other areas. It's a huge multi-headed issue in the US.