I really vouch for dogecoin as well. I have been using that coin for ages already whenever I want to transfer money from one exchange to another.
Maybe one reason that I can think of is that those exchanges that do not list doge is that because no dev is paying for the listing fee for this coin.
The maintenance of the wallet and other things cost a lil bit of resources from them so if they can't get anything out of it, they prefer not to list.
But if you consider those doge users and traders, they can already generate income from the fees involved.
I hope they will include doge as this is one of the most used coins in terms of transfer purposes.