Question: Why is there so much emphasis in the Yeshivish world to learn Gemara in Aramaic? Why can't you find an English artscroll shas in most charedi yeshiva?

It is not Lashon Hakodesh and it was written in Aramaic as that was the language spoken at the time but nowadays where English is the vernacular why should Yeshiva students be pushed to learn Gemara in an extinct language.

Answer: 
Aramaic is actually one of the biblical languages (Daniel, Ezra/Nehemia) and even has words in the Pentateuch (e.g. "*ygar sahadutha*" by the treaty of Lavan and Yaakov). The Maharal interprets the unique significance of Aramaic and advocates that *shnayim mikra v'echad targum* specifically employ *Targum Onkelos* for this reason. (In seeming contrast, the *gemara* in *Bava Kamma* [at the end of *Hachovel*(?)]) criticizes those who combine the language of the Babylonians with Hebrew [i.e. the classical version of "Yiddish"] so this likely is irrelevant since the Babylonian tongue alone is advocated there.) Nonetheless, there is certainly a solid argument to be made that if the language comes at the cost of the *lomdus*, the *tafel* has replaced the *ikar*.
It's helpful if said bochurim plan to learn almost any post-Talmudic Torah literature too. Commentaries on the Gemara, commentaries on Shulchan Aruch, responsa, and much else use a lot of Talmudic expressions.