For those that don't know me, I have kind of become the main Community Developer for Mongoose Traveller content for Fantasy Grounds. I don't work on the ruleset, I just convert PDF books for use in Fantasy Grounds. I don't work for SmiteWorks, I volunteered (commission-based) to do this out of love for the game.
I have been playing RPGs for a long time and running my various RPG campaigns on VTTs for over 20 years. I started using Fantasy Grounds way back in 2006 before they had any officially licensed products. I am pretty sure it has, by a long stretch, more official content available (over 4000 books) than any other VTT available today. It is not hard to use. Out of curiosity, I recently tried Roll20 and Foundry. Roll20 was ok, but the content is just not there and I don't like the online-only aspect of it. Foundry is...well...I did not like it and could not even figure out how to get anything I might have created into the application. Sure, it has some flashy graphics and such, but I think that is generally just a distration.
From a Mongoose Traveller 2e perspective, by my count there are 116 books in print (may be off by a few), Fantasy Grounds has 70 MGT2e books available today, 20 of which I converted just this year alone. With that much content available, I can't image playing anywhere else when you are going to basically be on your own trying to get stuff into whatever other VTT you are using. I highly doubt the converted books for other VTTs will be free...if an when they ever get done. There are a few availble for Roll20, but those cost money too. I have taken about a month off from doing conversions, but am starting to get back into the swing of things today with work on the updated High Guard 2022 Update book.
I don't know what goes on between Mongoose and SmiteWorks (The FGU owners) with regards to how they price things or offer discounts. But, I have always felt, in whatever form you want to run RPGs, you have to spend money, just like any other hobby. As the GM for my groups, I accept that and will spend what I need to continue to play. If I need books, I buy them. If I also need them for a VTT, I buy them there as well. If I get a discount, great...if not, so be it. We do the hobbies we can afford. When I can no longer afford to buy content, then I guess its time to accept that or find a different hobby.
The new Fantasy Grounds Online Reader tool (still in Beta) for your library (read: purchased content) the was announced yesterday by the FGU team is a really helpful tool that allows you to read books you have bought right on the webpage without the need to fire up FGU. This is not the PDF, but a slightly reformatted version of the Reference Manual that GMs use in FGU. They don't have all the books readyyet, but more will come online soon.
One other amazing recent development for FGU is another dev recently release an Extension for FGU called 'Traveller-Extended' which is a huge QoL improvement to the ruleset when it comes to Vehicles and Weapons in the Combat Tracker and Spacecraft combat. Not having the ability to effectively use Vehicles in combat has been a huge missing feature for quite a while now, so this capability is very nice.