No reason for them to rush while GTA Online brings in so much money. It's not like back in the days of GTA 4 where some extra money could come from DLC but the next actual big paycheck would be a sequel. Especially when producing some cars and guns for GTA Online isn't going to take many resources compared to a full game and can generate a huge profit once they slap a massive in-game price tag onto it that funnels players into buying shark cards, plus there's GTA+ which is a subscription program for GTA Online too.
For an example of how much profit a simple car can generate, the most recent update has cars that would require a purchase of $20 - $50 in shark cards to get enough in-game cash to buy just one of them. Even $10mil in-game cash that costs $100 won't get you very much really, and I'm sure there are hundreds of people who throw down money on those things to buy stuff in-game. I tried playing GTA Online when it first launched by just earning money in-game and it was an awful grind, and back then nothing cost close to what things in-game do now. If the game nowadays isn't one of the worst grinding experiences on the AAA market I'd be impressed.