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: 
According to Tiferes Yisroel the gemara was redacted multiple times by Ravina and Rav Ashi. The reformatted the words to make them more contemporary. The Masechtos they didn't get around to have uncommon words. But apparently even they didn't pull off a complete switcharoo.

Over those centuries Latin and other languages were interpolated. But no complete upheaval of the language.

Many times authorities are unsure of a word's meaning, and that word has halachic ramifications. We can't just get rid of the original and replace it with our possibly flawed translation. We must study it to become experts in it.

One example comes to mind is Rabbeinu Tam in Seffer Hayashar talking about business transactions on Chol Hamoed. He points out that Chazzal disallowed Prakmatia, a word only used to connote a business transaction, not personal acquisitions. This is a subtlety that might have been lost had someone previously translated that word into a more common, respectively modern, language.
To expound on Loewain's great answer. You see Aramaic in each Corpus of Tanach (TaNaCh). In Torah as Loewain pointed out the Torah (Book of Genesis) says when Lavan and sons were chasing after Yakov and family, the Pasuk says the 2 made a "Peace Treaty Memorial" by gathering a "Heap of stones" and Yackov called it "Gal Eid" (Hebrew for "Pile (of stones) (should be a) Witness (as to the fact that we made a Peace Treaty)and Lavan called it Ygar Sahadusa (Aramaic for same). In The Corpus of Neviem (Prophets) there are many words in Aramaic.In the Corpus of Cisuvim (Writtings) Ezra (I don't think 2nd part- I.e. Nechemia) has several entire Verses on Aramaic; But the Book of Daniel has the Most, even Chapters of Aramaic. (Interestingly, the Aramaic is mostly only written down when the players in the Book spoke or wrote on Aramaic, and we are quoting them or reading or writing thier Letters.
I believe it was The Ramban that wrote that Aramaic is a Holy Language, and in fact our Forefather Avraham spoke Aramaic. (As he was from Or Chasdim in Babylon which explains why Lavan who came out of that family also spoke Aramaic, as well as the Chaladians in The Book of Daniel. However, since "The Men of the Great Assembly" edited and organized some Books in the Corpus of "Writtings" (Daniel for example Did write the Book of Daniel in a Rough Draft sort of format, as did Nechemia, however, "The Men of the Great Assembly" (71 members whom according to many; All served in the Great Sanhedrin of 71, either before the 1st Temple was destroyed, or after the 2nd Temple was built, they also had the last three Prophets amongst them) wrote the Final Draft, through Prophesy & Great Wisdom Consensus, they decided to write Aramaic whenever the Character did in fact speak in Aramaic. The Ramban (Nachmonides) explains that they did this because it's more accurate to have the real words used instead of translating it into Hebrew. They could do this now, he writes, because the Jews now, after having lived or still living in Exile Babylon can read Aramaic!