> Why do people support a single company (like in this case Uber) taking over the business of thousands and thousands of existing companies and hence monopolizing an industry?

In many cases (in USA at least) the industry is already a monopoly as it is. Uber is coming in and offering an alternative which is way better than the current yellow cab system. In many cities in America, getting a cab at 2am after the bars get out is nearly impossible due to demand, so you end up walking a few miles home because it's quicker than waiting around for a cab. Uber and Lyft have largely changed that. Furthermore, I don't think that there is some strong allegiance to Uber or anything, it's just the largest company of it's type now. I quite enjoy and use Lyft as well, and would definitely be open to anybody else who wants to enter the market.

Taxi companies may be small mom and pop businesses in some areas, but in most large cities in the USA, they are breaking the monopoly, not creating it.