There's a reason why Oblivion, Skyrim, Fallout 3, Fallout Las Vega, Fallout 4 were successful single offline games without online. There's a reason why Fallout 76, Elder Scrolls Online are failed cause they were focused on Online because of the trend, microtransactions era.
GTA 5 Online are just lucky that everybody plays. More reason why people love Red Dead Redemption 2 offline story mode and hate RDR 2 Online.
To be fair, GTA 5 Story Mode was a little bit disappointed along with Fallout 4.
I feel like they're getting lazy these days now. I hope they don't fukked up with new Elder Scrolls Game and I wouldn't be surprised if they fukked up GTA 6