Hundreds of millions would be a lot. I think you overestimate the demand for something like Starlink a lot. People who can afford to pay and would consider paying for Starlink tend to live in well developed countries. These countries typically have internet connections which are better than wat Starlink offers. Statistically most people live in cities, which also typically have good internet. People who live in lesser developed countries and don't live in cities tend to not be able to afford or willing to pay for Starlink. Usually there are other cheaper options available, even though they would offer less bandwidth than Starlink. So the total market would not be hundreds of millions.

Starlink also offers poor bandwidth and latencies compared to local solutions. People who just use things like Facebook would rather have a low latency and low bandwidth solution than a high inconsistent latency and high bandwidth solution. Starlink is getting better, but the latency, especially in regions with few base stations (which is their best use case) will be inherently poor compared to wired or local wireless solutions.

Starlink themselves thought they would have 20 million subscribers in 2022. In reality they managed just about 1.5 million. (It's not clear how accurate these numbers are and if they include non paying customers) They could get more people on board if they lower pricing, but then they need more customers to get the same revenue. Since the costs of building and launching the satellites, managing them and maintaining the ground part of the system are fixed and high, they need to generate a lot of revenue to turn a profit.

There may be large parts of underdeveloped areas in the US for example where people have the need for high bandwidth internet and are able to afford it and local solutions are lacking. But you end up with only 50 potential customers for one area of which maybe 5-10 people actually sign up. As soon as you hit something like a town, local wired and wireless internet solutions will outcompete Starlink easily. In a poorer country there may be more people to be found in rural areas, but if you only make the equivalent of $5000 a year, you probably won't spend more than $1000 for Starlink. For those people the budget they have for internet would be more like $50 a year max.

And remember even if Starlink starts to operate at a profit, they aren't out of the woods yet. They have had huge upfront starting costs, much more than they expected. Those costs need to be covered before investers actually get anything.

All the while they are competing with local internet solutions which are being rolled out fast all around the world. Something like 5G is rapidly cutting into the need for something like Starlink. As soon as subscriber count starts dropping instead of rising, it's all over.