I just want to preface this with a statement that I do not work for Bandai, I am in no way affiliated with Bandai. But based on what I have seen over the last few years, they are trending towards moving big portions of their business direct to consumer, which makes a lot of sense:
The Gunpla lines are produced in 1 highly automated factory in Japan. There has been talk about moving some production out of Japan, but I believe this was met with pushback (maybe the China Red and other China exclusive items are manufactured overseas)
Their Tier 1 retailers are the big Japanese retailers (Yodabashi Camera, Bic Camera, etc.). Unfortunately, we have to lump Amazon JP into this list. I say unfortunately because they have extremely predatory practices when it comes to suppliers.
Tier 2: Overseas distribution partners, like Bluefin, who run the North America operation
Tier 3: The AmiAmi/HLJ/HobbySearch of the world: real, non-scalper sites cannot possibly compete with the tier 1s or 2s in terms of volume
This would account for 1st run, retail offerings only.
"Unpopular" offerings are done as special batch jobs, made to order, essentially and sold on P-Bandai. People see Premium Bandai and think the kits are premium. In reality, they are not premium, just made to order
Originally, P-Bandai was simply recolours, with extra parts, etc... They now do P-Bandai unique kits because it is just easier to manage shelf space. With the sheer volume of gunpla available, I am sure the Tier 1 retailers are pushing back
Maybe it was the Tier 1 retailers that said they would not devote shelf space to the F-90, which is why this one went P-Bandai despite a full colour box, new molds, etc.
Gundam Base is another outlet for retail kits. When you visit a Gundam Base, you will find pretty much every single retail gunpla kit ever made.
When you see kits being made for Gundam Base Web Shop, these are kits they are planning to make to restock the Gundam Base outlets, not for the retail channel. They open it up to pad out the production run so that they do not need to manage as much inventory
I started noticing more and more restock kits coming via this channel, rather than the retail channel
The Jan 2022 reissue of the HGUC Nightingale tells me that the retail channels do not want more stock for their shelves, probably because of the size of the box, the recent release of Xi vs. Penelope, the upcoming Virtue, etc.
This is all speculation, of course. I have no insight into Bandai's operations, just what I've heard from shop owners and recent trends in announcements.