The thing about multiplayer aspects about games is because you’re pretty much playing with new and different players all the time that every session is a different experience. This is versus single-player where once you’re done with the story and you’ve run through it a couple of times, that’s pretty much it.
This is also why it could explain the success behind GTA Online, and why there are rumors that Rockstar could have scrapped their plans for a single-player DLC in favor of maps expansions for GTA Online. This is according to a post on the GTA Forums that was made back in August but have recently come to light again.
According to the post by Softsecrets, “Single player DLC has been replaced with Online Map expansion model! Mainly due to the unforeseen success of micro transactions and GTA online in general!” Now obviously it’s hard to tell if the post is any accurate, but given that the post also included information about the Biker DLC which proved to be true, perhaps the rest of his post has some merit as well.
It is unclear if this means that Rockstar has no more plans for single-player content, but like Softsecrets said, with the success of micro transactions in GTA Online, it makes sense for Rockstar to want to keeping milking that cow, but until Rockstar can confirm/deny it, take it with a grain of salt for now.