You do realise that they probably had no say in the matter, right? It was most likely this situation or graduate completely.
And I think you missed the part where Country Girls are probably going to not be doing anything for a couple of years. It's not like they're doing the exact same workload in their new groups AND CG at the same time. The entire reason they're being shuffled around to these other groups is
because they want to stay active and do more than just sitting around waiting for the one time out of a year that Yamaki and Ozeki's schedules might allow them to release something. The Country Girls announcement said any new songs would most likely be digital only and they'd only participate in H!P concerts, which makes it sound like the group's basically dead (if only temporarily).
but I liked 'stable' groups like berryz and C-ute and I am longing for a new 'stable' Group to fall in Love with... Sadly H!P Doesnt seem to care about longlasting groups anymore.
And you're missing
the entire point of H!P groups. I hate to break the news to you, but Berryz and ℃-ute were abnormalities. Pretty much EVERY SINGLE H!P GROUP EVER (that lasted, lol) has had member additions (and graduations). The only ones that went, say, more than 5 years without change (that had a significant number of members to begin with) were Melon Kinenbi (at the time they were known for it), Berryz Koubou, ℃-ute and kinda Juice=Juice almost (although IIRC when they were announced they did say it was potentially a changing lineup).
Lastly:
THEY CHANGE THE LINEUPS LIKE THIS SO THAT THE GROUPS CAN BE LONG-LASTING. Guess what? Sometimes idols want to go and do other things. Sometimes circumstances don't work out and they have to leave for whatever reason.
You're in the wrong place, the exit is that way.
EDIT: Melon Kinenbi, Berryz Koubou and Buono! are the only long-lasting H!P groups that never added any new members. ℃-ute doesn't count because Kanna was added 6 months after the group was announced.