Ok,so first off, gta and red; gta is arcade, red is realism. gta has no limits on its creations, red is limited to historical facts, happending, atmosphere and events.
Are there alot more that could be added to red? ofc but sutch development takes time. Afterall, gta5 is 7+ y/o, red is 2. Red had covid in the middle of its existance while gta saw a natural drop in new content cuz they at the times had notingng new to add, and that was before covid forced workers to stay home.
For Red, they have to think hard about what can be added, plus it seems they have taken a stand that the game