I've drawn all manner of creatures, my favorites being some of the 'odd' ones. I have sketchbooks full of tapirs, pangolins, hoatzin, kookaburras, bettas, and on and on. However, I rarely (i.e. almost never) get commissioned for these pieces. Once in a blue moon I will get a commission from someone for something a bit more exotic (for instance I had an ostrich farmer have me make a piece with ostriches on a savannah for his home) but what I get is mostly wolves - foxes - sometimes bears, otters, etc.
Since I do this for a living as well as because I love creating art, I have to do what people want.
Why aren't the other species popular? I guess if they don't have the 'mystique' of being a big, powerful predator or a cute and little fluffy something, they don't get recognition for most people. I don't think there's anything wrong with any animals, popular or not, but you're definitely likely to see some more than others, always.