The problem with long development times is that you end up re-doing a lot of the work over and over and over again. Things like the game engine changes - the one you start with gets obsoleted and now you have to waste a couple of years switching to a newer engine (this one has impacted games far more than anything else, really). Along that is well, changing technology that makes what was once cutting edge not so much.
After all, 10 years ago you were kicking it with 1080p graphics, then it went to 1440p, and now 4K and even 8K. This sucks because it means your assets need to be similarly upgraded - what looked decent at 1080p looks OK-ish at 1440p, and starts looking pixelated and such at 4K.
Things like this suddenly mean you've just wasted 3-4 years basically re-doing the game all over again
It's not an easy decision - do you try to go for that One Great Videogame To Rule Them All, or do you compromise your vision and release a bunch of smaller videogames that are smaller in scope but at least doable and if they sell well enough, issue a remaster a few years later using newer engines to take advantage of new technology? It's hard because visionary game designers want the One Game, and splitting things out feels like an ugly compromise. Also having a near unlimited budget makes it even harder still (half a billion dollars is a gigantic budget any any measure.
Even worse now are rising expectations - everyone's got ideas what a game costing half a billion dollars should look like, and with half a billion dollars and over a decade of development, it had better be good.
Of course, I think at this point, "release" is probably misguided since everyone who paid in gets regular updates and demos. At this point in life, it's probably easier to just treat them as an ongoing subscription and updates and adjust as the community adjusts. The game's never going to get finished, so let's polish it up, release it far and wide and let everyone play and continually improve on it. It's basically what's happening nowadays anyways. A not quite MMO thing