Rockstar was very open as to why: PC players are a fraction of a fraction of their income. Xbox One players (yes, the previous gen) give them more money than PC players for GTA Online.
I could imagine PC gamers are less interested in online and the whole shark card thing though. IMO that's really damaged the GTA experience.
Though I rarely game on the TV, for me it's uncomfortable.
I was too fixated on a classical gaming PC with mouse and keyboard.
- Steam's Big Picture mode works, but there are lots of sharp edges (launcher support being the biggest).
- PC versions of games frequently have no way to switch to a couch-friendly UI (loading menus designed for PCs)
- The power management and hardware setup is not at all streamlined
- Controller management can be painful
- Streaming apps mostly need to work in a browser, which won't have controller support.