Maybe because it is live, unlike the other shows... and maybe because there's still a pretty good enough audience for RAW, unlike the other shows that they prefer to keep it exclusive to the USA Networks and in turn, for their sponsors.
They could air it even if it's live. I've watched the ppv webcasts on WWE.com before so I don't see why they couldn't air something live. The reason they don't do it is because the USA network won't let them or they wouldn't like it if they did.
If you miss the show just watch a few days later on Mun2 or the AM Raw that comes on USA network. If you don't have a tv then find a live stream or just catch as much as you can on Youtube later. Raw is so shitty right now that watching live on a monday night should be the least of your problems your having with wrestling right now.