It’s unfortunate that the Y label isn’t marked, it’s behind a paywall that I don’t really feel like paying for, but here’s a comparison of the additional revenue generated from the sale of DLC in GTA Online for consoles vs pc. Remember, the only thing they sell is in game currency. Even if we assume that the data on the left is in increments of say $500,000 or $1M, it’s clear that PC sales of in game cash cards aren’t making anywhere near as much as the ones on console.
There also the point that GTA V sold 5M copies on PC. That’s under 10% of total sales as it did 55M on the consoles. Even if you split it between four consoles and assume they sold an even amount, every console sold twice as much as it did on PC.
My guess, based on not much other than that graph is that they’re prioritizing the console versions. Then once they’re up and running with RDR Online and the money starts rolling in from that, they’ll look at porting it to the PC.