TL;DR: price, performance, traffic leaks
Vimeo suffers from many of the same performance issues as YouTube, taking much longer to start playback and buffering far more often than SmartVideo. Vimeo also requires you to upload all of your videos to their site and use their embedded player.
The SmartVideo player is free of branding, marketing links, and other traffic leaks keeping your visitors on your website, focused on your content. Vimeo does not become "white label" until you spend a minimum of $240 annually.