Evidently, by today's physics, you cannot be in multiple places at the same time and while it doesn't sound compatible in gaming development, this is the only thing I can think of for Rockstar Games.
Rockstar Games practically confirmed strong rumors that have all their development teams committed to the development of Grand Theft Auto VI and while rumors stated that Red Dead Redemption and Grand Theft Auto IV were next in line for remaster games for this gaming generation, they did acknowledged that REd Dead Online is not gaining more new content on par to Grand Theft Auto Online.
Now, Rockstar was specific to say that while new content is not expected for Red Dead Online, the service itself is not canceled and will have proper seasonal activities and festivities.
But as to incentive with brand new assets is probably now out of the picture.
About the RDR/GTAIV rumor, it was suggested that not only GTA VI was a main factor in rollback efforts, but the feedback postlaunc of the Grand Theft Auto Definitive Collection left a weight on Rockstar Games's decision on not risking more flops.
But of course, Rockstar did say that they will be working to improve the overall GTA Online experience with new gameplay updates, adding top community-requested experience improvements and upgrades to make it easier for players to enjoy everything GTA Online has to offer.
Via Rockstar Games