User blog comment:Mckrongs/Monster Hunter 4 for the Nintendo 3DS/@comment-5648643-20130917145242/@comment-1011548-20130917154151

The monsters that appear in a MH game has been very very arbitrary for a while. Tigex and Narga both come back for Portable 3rd, only for Tigrex to not appear in 3U... then it comes back as almost the second flagship in MH4. Meanwhile Narga does P3rd and 3U straight, but isn't in MH4. Akantor and Ukanlos return for P3rd, skip 3U, then only Aka comes back for MH4 (as far as we're aware). MH4 has all the old 'dromes apart from Giadrome, and randomly throws Great Jaggi in the mix but none of the other 3rd gen raptors. It also has no raptor in the Frozen area at all. It also brings back Kushala and Teostra, but not Chameleos and Lunastra.

I think Capcom's policy when choosing a returning monster roster for a game is just closing their eyes and throwing darts at a list of names. ;-)