The Issur to leave Eretz Yisrael is not a blanket one, there are leniencies, especially if one wishes to return afterwards. Indeed we see many Amoraim who left Eretz Yisrael to go to chutz la'aretz, including Rav, Rav Dimi and others, who wished to study or teach Torah in Bavel. Chazal however wished to discourage people from going even for these reasons and therefore they made an extra Gezeira, according to the Meiri's view. According to the views that even Olei Mitzrayim is included (see further), even though technically its not Chutz La'aretz they wanted to discourage going to these areas since many Goyim lived there

Additionally this Gezeira has ramifications for a Kohen who would only be allowed to go for study or to marry or another important Mitzvah and only if he cannot perform these in Eretz Yisrael. This issur was established during the time of the Beis Mikdash and may have been primarily aimed at Kohanim in order to prevent them leaving and therefore not being able to perform their duties in the Beis Hamikdash.

Regarding the matter of Olei Bavel and Olei Mitzrayim there's a dispute between the Kaftor Va'ferach and Rashi, with Kaftor Va'Ferach maintaining that even Olei Mitzrayim (e.g. Sidon) is not included in the gezeira and Rashi, Rambam and others disagree. However most of Ever Hayarden is included in Olei Bavel's conquest and there was a flourishing Jewish community in the Golan so this would not be included in Eretz Ha'Amim for this Gezeira.

Yoel Domb