That's probably because animating any form of graphic shirt is difficult and most likely deemed unnecessary. The only studio that I have seen to-date that has animated graphic shirts has been Polygon Pictures, and anyone who has seen their animation knows that they use CGI.
((Spooky Jim)) "Hey. I'm Josh. I'm in a band called Twenty One Pilots. Yes, I love food. I'm an extrovert. I have a sister named Chase or as I like to call her 'spooky chase.' I dye my hair all the time. Come say hi!"