The problem with VNC is the same as the problem with IRC. The new user experience is trash. They're both on the level of protocols, like SMTP is, so you get variable support for user quality of life features and users bounce because those features aren't built into the protocol. For VNC, it's per window support and image compression format/acceleration. For IRC it's pre-join-history scrollback, and anything you need a moderation bot for. SMTP's problem is spam. (Doesn't matter if that's a problem with the protocol or the wider situation and should be managed at the application level, it sucks for users.