At this point Re-Logic is more of a chad game company than Mojang. Re-Logic always listens to their players' suggestions and 99% of the time they think that idea is a great idea, why else has Terraria gotten the popularity it has today?
Theres lots of time that goes into mobs like ideas, designs, features, and new blocks. The reason why people mod them fast is because they just copy them
-Crab extends reach (can be useful for clutching)
-Armadillo gives wolves armor, giving them better defense
-Penguin speeds up boats, which are good in getaway situations
Crab:
Well..good
Armadillo:
uhm I mean cute bu that stop here...ppl use wolves in 1survival/1194958248
Except those who are cool enough to use them everytimes
Penguin:
yeah but..dude..polar biome only..
Tell me how you will get in that situation if you players never go in this biome =.=