It's that UF management doesn't want to spend the money needed to make their members/groups more popular. They want the popularity to come to
them, rather than having to pay money for things like TV show appearances or CMs or billboards or whatever else.
Honestly, UF are too financially conservative at the moment. That's one huge difference between Tsunku-run H!P and current H!P - Tsunku was willing to take financial risks in order to see if things worked, and even though a lot of the time UF probably lost money, there were a few cases where it paid off.
Hell, MM。
itself was initially a risky investment
. Sharan Q just kinda came up with the idea, went with it, and, well, here we are 20 years later. But it very well could've been a one-off thing, the group could've petered out after a couple of years, etc.
Part of the problem at the moment I think as well is that they've got such a small pool of composers/lyricists to work with. When Tsunku did everything (or most of it) it was one thing, but when it's multiple people you have to divide up the work. Although, I do wish they'd just hire Hyadain full time because out of all the composers his sound is the closest to Tsunku's, but he has other commitments, obviously.
Soloists also just don't sell as well anymore. You have to have a big agency/label backing you and willing to push you to get anywhere. A potential semi-solution would be having someone like Airi or Sayumi doing anime tie-up songs to get exposure (and H!P's ventures in that area have always performed very well). Since Sayumi's been in an anime, albeit a web one, there's always that...