Didn't mean you had to complete but I think they said the average was below 40%
This. They have the statistical data to back this up. They are a business. I think the people complaining about lack of SP dlc represent the minority. The majority of people play single player once and then hop online with their friends, so why wouldn't they cater to them more?
Isn't GTAV still a top 5 most played game online for consoles?