Okie dokie, here's a probable reason why.
I own and admin a "regular" forum (not a gpt forum any longer). Even there, excessive emoticons, images, just about anything...can run up the queries, add files, run up the bandwidth, etc. if everyone does it. We also have a rather large gallery, and an Arcade, and I'm forever cleaning out our server which is a pain in the tookus. LOL Although we do allow a goodly amount of usage and I'm constantly loading in more images for members to us, it does become a chore. And it can be costly. And when someone posts a LOT of extra stuff...it's tough.
Here, the forum is part of the site and considering the amount of people both working the site and posting in forum...it can really add a lot of extra work to keep the tables clean. So while CS is nice enough to allow us to post images and emotis, I think we should do our best to limit ourselves on how much we use when posting.
Just a lil explanation.
edit to add: Plus with tons of punctuation marks, things start becoming a bit confusing. And can run the subject line across the page (not sure how it works here but on most forums we put a limit on amount of characters).