BTC-e probably doesn't add coins on a regular basis in order to avoid stuff that happened to cryptsy (if their story is true).
They only use seriously vetted software to make sure nobody gains access to their systems through leaks in the wallet software.
Not sure why they added dash, but then again, it is one of the higher volume coins so that is probably the reason.
When BTC-E started (back in 2012 I think), they added all the alts in existence at the time, even devcoin was there. I think the last alt to be added was Feathercoin in 2013, and they removed some of the older non-performing coins.
Then they stopped adding coins. Doge started in Dec 2013, when that huge bitcoin surge to $1000 was building, but I think BTC-E decided that Bitcoin was going to break out and there was no more need for alts, and refused to add any more (and didn't add doge).
So it means they've changed their mind in a fundamental way - they arn't sure that Bitcoin is going to win, and they're hedging their bets...
All we need now is for Coinbase to add alts and we know that there is trouble brewing for BTC.