It's useless coins, toys for a short time. Poloniex not add to itself coins like this, so as not to create conflict with the law.
You mean coins like POT that are listed on Poloniex? I think most of the pot coins are stressing their intent to partner with and build services for legal dispensaries.
POT are listed on Poloniex a long time ago, when Polo was small exchange with low volume. Now they operate strictly according to US law. I do not think that they would want to spoil their reputation for the sake of adding another fork without future.
You means except for rampant market manipulation, trading on inside information, trading against their Customers by closing wallets during pumps, etc.
It seems Polo only cares about making as much $$$ as possible before Polo becomes obsolete... and is "hacked" and disappears.
With small XCI cap Polo is a pipedream anyway...
Unfortunately, Yobit does not support CryptoNote (and MAR has paid to be listed there soon).