@ApplejackFan204  
Because these creatures aside from Capper are creepy, ugly, strangely, tough, and infested. These creatures in Klugetown are some aardvarks, fish, lizards, lizardfolks, reptiles, reptilians, porcupines, rats, naked mole-rats, mice, sharks, turtles, tortoises, pigs, boars, hogs, warthogs, moles, tapirs, anteaters, hedgehogs, bats, amphibians, some goblin-like creatures, some rhino-like creatures, and some creature hybrids.

@neo4812  
The show, the comics, and the movies all have implied that the world these characters live in is pretty large and vast with a variety of different creatures. But non-ponies tend to stick to themselves in their own countries for the most part. What Frustration in Excelsis said has a lot of weight to it.
 
As for Capper’s appearance, his design was once drastically different from what it used to be now. In earlier concepts his name was Mendax and his older design was more odd and alien looking. He basically had a fox like face, four eyes, talon like hands, and a tail that was kind of a cross between a scorpion’s stinger tail and a pincer (or secondary mouth).  
 
As for why this old design was ultimately scrapped for his current design, it could be a multitude of things at play here. Perhaps the design was too hard to animate or perhaps the design didn’t translate well into a toy (both of which applied to the very detailed scrapped concept designs for the seaponies and hippogriffs). Perhaps the higher ups didn’t like it or children thought it was too scary (or they assumed the design was too scary for children). Perhaps they wanted to play it safe and chose a simple anthro animal because many other studios were doing the same (e.g. Kung Fu Panda, Zootopia, Sing, etc.). Or perhaps they chose an anthro brown and tan cat design as a nice little call back to Catrina from G1.  
 
It could be a multitude of the above guesses really.

The first thing this scene reminded me of was the Pied Piper of Hamelin.
 
@neo4812
 
I mean, Klugetown is on the other side of the world from Equestria by all appearances – if we assume their world is the same size as ours, it’d be like going from the middle of the U.S. to Brazil, but without any roads or ship routes and having to trek across deserts and wilderness most of the way. It doesn’t surprise me much that you don’t see abyssinians in Equestria, or ponies in the southern lands.

@ApplejackFan204  
I think its established that the world that the ponies live in is far lager then the average world and has way more creatures not seen by ponies. that or the creators are lazy and just threw in cat creatures in because they thought it would be cool

@neo4812  
Giant dog creatures exist. So there must be giant cat creatures.

@ApplejackFan204  
that’s a very good question

Why aren’t there creatures like Capper on the show?

“Oh, we march from here to there! And it doesn’t matter where! For to march and drill over… uh, what else rhymes with ‘drill’?”

those legs. such a cute walk cycle

the pied piper of ponies

@luna’s husbando  
Toy, I think.

“Dapperpaws” When was his surname revealed? The movie credits? The prequel comic?