Mattlock and his friends are magical creatures and can shapeshifter into a humanoid form (among others).

They retain their animal ears and tails in human form. These animalistic features are visible to humans and so when trying to blend into human society, they have to conceal themselves. This leads to them wearing a lot of hoodies and hats and baggy clothes etc.

Except for Rorshak, who doesn’t bother entering human society and so he wears whatever he wants, which is usually very little haha