Perhaps you included this in your DRM comment, but I think the biggest issue is anti-cheat. Most online games with a sufficiently large 'competitive' element require a kernel-level anti-cheat which won't work on Linux.
My understanding was that EAC works in userspace mode on Linux, instead of at the kernel level. So, you can enable it, and it'll block the most easily detectable of cheats, but it's not very hard to bypass.
Then again, kernel-level anti-cheat is not that hard to bypass with special hardware, either. I guess someone ran the numbers and decided that blocking some percentage of cheaters at the cost of blocking 100% of Linux users was a worthwhile trade.
Vanguard doesn't work, and perhaps that's for the best.