It is a fair move. It can be expensive to run the right infrastructure per coin and you would start to incur losses with low volume and especially on coins with broken blockchains.
I think it only makes sense for Bittrex to removed coins that are not performing well. And this is no big issues, other exchanges also do it. I remember has last year there are some big exchanges who removed or delisted a lot of coins.
The only drawback I heard then is that exchanges didn't informed dev right away, that's why most of them are caught unaware of the said actions and most of them are arguing that they are still doing development at the background that's why the project seems to be quiet.
Of course the bittrex has done a very mature analysis and thought. Removing the coins from the list they have there must be a very strong reason. Most are coins that are not developed yet, although Bittrex is known as a tightly qualified exchange to include the d exchange list, but we do not know when a coin will experience a decrease in performance. This is something reasonable and Exchange Bittrex has started to remove coins that do not have the potential for the future.