Satellite internet is a good way to avoid a lot of trouble building the ground infrastructure necessary to reach regions of the planet where logistics turn out to be very expensive and accessibility is highly limited. Until now, there was little care about the population of third world countries having internet access since it was perceived as a commodity in the first world.
Expand consumer markets to third world countries
For companies like Amazon or Apple, which are evolving to a market where consumers can buy their products online, the idea of having millions of sub-Saharan Africans connected to the internet starts to be seen as highly profitable. A company might have a lot of trouble building and maintaining shops in these areas but might be totally capable of moving products to consumers on the net. They would out-compete the local markets with this strategy. Having satellite internet is one easy way to do that since building and maintaining fiber optic cables in those regions might be more expensive and unreliable than lunching hundredths of satellites into space.
Expands military applications in third world countries
For the US there's a clear need for higher broadband internet in these regions. After all, the US has a military industry that usually operates in third world countries and has a lot of difficulties creating the needed infrastructure for communications and fast data transfer. These regions are not only problematic because of the little connectivity and infrastructure they have in the first place, but also because of inherently geographical issues (mountains, absence of roads, etc...). There is also the thing that these places where the US intervenes are war zones where building a fiber optic cable is very difficult and life-expectancy for it is small to say the least. The US military now needs to connect to drones and download high resolution images with loads of data, all in real time to be able to make quick decisions and control aircraft like a normal pilot would. The US military therefore needs high speed internet just like Romans needed roads for their military transports all over Europe, and satellites can provide those means. Satellites all around Earth are subject to the same predictable environmental problems, they are not going to be sabotaged and you don't need to make specific studies for drilling and laying of fiber optic cables in different terrain. Also, ground internet infrastructure will be abandoned when war ends and the US will need to build that infrastructure again in another place of the world it might want to fight. Satellites move around Earth constantly and thus the change in battlefield would have all the network infrastructure instantly moved if needed.
High-frequency trading competitiveness
This is interesting, and is something that has been explained on the Real Engineering YouTube channel. High-frequency trading is essentially a very interesting trading technique on modern markets. You buy and sell corporate shares in terms of milliseconds to have huge amounts of incredibly small profits. It's a cumulative operation that yields millions of dollars in the long run. For these kind of investments to work, there are financial corporations that work hard on creating fast algorithms that can predict ephemeral trends and invest autonomously in the blink of an eye. The main problem is how to connect London's market and New York's Stock Exchange. For now they use the optic fiber cable of the Atlantic, the "Hibernia Express", which allows for transferring data at the speed of light between the two places. The delay is around 58.95 milliseconds. In principle this is incredibly fast, but the thing is that the fiber optic cable has a certain refractive index that makes the speed of light slower than the speed of light in a vacuum. Even if the path length of a signal through a satellite network would be a bit longer it is way more profitable since the delay would shrink a few milliseconds, due to the signal travelling most of the way in the vacuum of space between each satellite. This difference of just a few milliseconds is enough to give an advantage to the company that uses it over the ones that invest in high-frequency trading using the Atlantic optic fiber. A few milliseconds is enough for a company to want to invest millions of dollars in building this huge space infrastructure, the profits for them are going to be way larger than that.
The whole idea has been advertised as a democratization of the internet, but something as expensive as building an entire satellite constellation needs economic incentives for sure. For making this "democratization of internet" a profitable endeavor these companies are actually thinking about what would make them grow and make them earn more money (because if they did this by pure solidarity they would just disappear and we wouldn't be talking about them by now but about the ones that choose to do it for profit). The driving force for satellite internet is in essence a combination of American imperialist and worldwide capitalist interests. No surprise that this is been advanced by private companies.