4U is the only time we've only gotten the G version of an entry. I seriously don't get why people act like it's some traditional thing.
We got MH1, we didn't get MHG, we got Freedom which was a port of MHG.
We didn't get MH2. We got Freedom 2 and Freedom Unite.
We got Tri and 3U. Skipped Portable 3rd.
Which brings us to now, where we skipped MH4, got 4U and Generations.
We've missed a grand total of four games in the main series, and only 4U is an example of only getting the G version.
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The real reasons I'd say there's no reason to expect an expanded X/Gen would be that the entry is in itself unusual, as an extra entry in a generation, and that there's been no Japanese announcement even though it would probably be coming out in 3-4 months if it was a thing.
Edit: It is unusual that there's been no main series entry announced for Japan yet for this year, though. They've yet to go a year since the series began without a main series entry in some form.