Most people don't realize that it takes about 400-600 hours of work to convert the average WotC book into Fantasy Grounds format. Also, there is usually EXTRA stuff, like automated table and encounter makers, etc. Like fo rexample the Dungeon Master's Guide has an Item forge where you can combine (magic) items to make new items.
Also, SmiteWorks (makers of FG) charges only about half the cover price of the book for the VTT version (which is a GREAT DEAL) and most of that money goes to WotC for the license anyway.
There's part of the issue: If they went about things differently, the amount of labour to integrate new things (especially those primarily relying on existing rules albeit in different combinations or with different flavour) would not be so lengthy. I have no doubt it could take that long for a VTT upgrade to support significant changes now. There are, however, things WotC could do in their development process that would allow them to distribute electronic artifacts (like databases of character construction, gear, magic items, spells, etc) simply as a fairly easy export. That same approach would vastly speed up creation of reference books by scripting. (I've done this on a military project - reference documentation needed a template then it just pulled all the particular reference data out into tables and sections based on export rules).
D&D Beyond likely also pays a good chunk of the $30 for the PHB for licensing - their integration work is probably less than FG though.
At the end of the day, it does not matter to me as a consumer (and not because I don't care, simply because of available budget) why a platform or its content cost significant chunks of $$$, it only matters that they do cost significant amounts. If I had $130 CAD to throw at each new book ($60-70 for the book, the rest for digital stuff, maybe even $150 CAD if I wanted a PDF of the book), I would not be that averse to paying it, but I don't. By having the price point they do, they price me and I'm sure others out of the market.
When I started playing this game, a hardcover was $15 CAD (DMG $18) and modules were $8-10 CAD. Now hardcovers are $60-70 and modules are released as adventure paths for at least $50 CAD. That's a five fold increase in about 40 years. Real wage growth hasn't matched that.
Frankly, I settle for cheaper production values (no fancy glossy pages, no super nice art, simple B&W maps and simple layout) a) because it is cleaner and often more usable at the table than the stuff in the expensive hardcovers and b) because I can't justify spending so much on the hardcovers. The creative content can be just as useful to me (I've met duds in both formats and great work in both formats).
Ultimately, the best value to me is having a lot of different module offerings as each new campaign has a new setting and only some modules work in it. $100+ per module path would leave me with thousands of dollars sitting on the shelf, vs. a few hundred in the cheaper production values.
I mostly want to steal segments of a module, good ideas, or use a particular single module that fits my games' geography or themes... whole paths are rarely followed.
What WotC produces now, other than reference books, is of limited use to me. The older D&D modules were more useful as are some 3rd party publishers' output. Also note that even with the reference books, I still depend on DTRPG and DMsGuild contributors to produce useful versions of the reference material due to the hardcovers being too arty and the data needs reformatting for utility at the table.
YMMV, but I'm not alone in wanting good ideas and relocatable modules with more modest production values. I do respect that others want other things, but I think WotC is letting a pool of money it could be capturing now go to other companies.