Because Mint has been horribly broken and useless from the day Intuit bought it. Currently I use an excel spreadsheet in lieu of my now-inactive Mint account. Because even nothing is better than mint.
Odd, I hear this complaint all the time but have never personally experienced it. Mint has always worked for me, even with a bunch of esoteric 401k and other accounts from no-name banks.
I had the same issues with Mint, it was always broken, always giving back unreadable account errors, always missing stuff in searches, never applying tags properly (and no mass tag update, argh).
Check out PocketSmith. It may not have every feature I want, but at least it actually works. There is a nominal monthly fee associated with it, but well worth it if you want to actually use an online money analysis tool to do anything.