You can't fault just the company, it's mainly a majority of the playerbase that is at fault here.
They keep playing and spending on that very same game, the interest doesn't really go down by a hell lot and revenue apparently still being sky high. also where talking one of the biggest game series in the world so apparently that revenue stream is still a crap ton perhaps not to far off compared to when they release a brand new game if not more. also where not talking any playerbase, where talking the huge mainstream playerbase you can't really get much bigger than that.
thus adding additional content and keeping it online is pretty much doing what most of your consumer base wants. If people actually lose interest and quit playing/ spending on this game or if a sizable chunk actually fell off to make the extra profits of a new game worthwhile They would have made a GTA 6 ages ago. I don't see this as rockstar being greedy because they are technically doing what most of the playerbase wants atm otherwise people would have left and played other games instead since they would have gotten bored of the game by now. The consumer base seems satisfied with what GTA V is atm. sucks for some but apparently the majority ain't really on the same page as people who want A GTA 6 already.
Sure you got plenty of people complaining about wanting a next entry but what does the reality actually look like if where talking the entire playerbase, not to mention that the online community can seem really huge but that's mostly because they make allot of noice, most people don't really share their opinions online, Pretty decent odds that the people who want the new stuff are in the far minority.
You do however get a small taste of GTA 6 with the additional content that is being added to GTA V I guess.
A lot of games are online only now. GTA Online and Fortnite both have a ton of frequent content updates that are supported by people that choose to pay.
People will pay hundreds eating at fancy restaurants and that lasts about an hour. Paying for optional content in an online game that will last over a decade seems like a good use of money compared to a lot of other ways people spend money.
The argument can obviously be made as what has value changes from person to person. To give a bit of background as to why I believe online only games are a waste of time and money (not just their outfits and other extras), it goes back to Warhawk on PS3. I absolutely loved Warhawk. Loved it. I dropped hundreds of hours into it and it was a favorite of mine for the entire generation. Then they flipped the switch and the game was gone. I still had the disc but as soon as the servers were shut down, the disc was worthless. To me, it felt like getting robbed of something I had invested not just money, but time and effort to get good at and enjoy. All they had to do to avoid that issue was add a competent single player campaign. It was when Warhawk got shut down that I knew online only games were a waste of time and money.
I don't agree with that way of thinking, you got to see online games as just having a fun experience at the time. Besides everyone moves on from a game at some point because of other priorities etc. There will be periods where people will be less active or just leave the game. life and it's events happen. Online experiences will rarely last forever unless the community stays really active. however even within those people will come and go. The game might be gone but the memories of fun times and experiences won't.
also if where talking money, if you did spend 100's of hours in that game and they brought fun you got a pretty awesome deal. With what other medium can one spend 40- 60$ for 100's if not 1000's of hours of entertainment it's a bargain at the very end of the day. very few things that cost money that will match that value wise.
I get allot of people here want stuff to last forever but these games do have plenty of value in terms of experience. All good things end at some point. Imagine MMO's that have pulled the plug 10+ years later, plenty of folks that still had great memories during those times instead of just feeling robbed. Allot of those folks just look for alternatives to get simular experiences again. Just my 2 cents.
Bigger Ip's and especially their biggest seeries do have a higher shot to last a hell lot longer online than smaller games, bigger companies and just more consumers behind it. Might also be something to take into consideration. and if it's peer to peer vs, ridiculously high odds of it still being playable online when official servers are down.