Why is this happening?
Because the internet for writers is a combined publishing news service/information update/gossip hub. Savvy writers read and listen and see what is happening, and they don’t like it. They don’t like the low advances and the way they’re expected to do the marketing themselves, so they figure they might as well do it all anyway. If you were an author with a popular blog and a lot of followers on FB and Twitter, wouldn’t you consider it?