That appears to be correct. It makes sense to me that Konami could've had a limited agreement with EGG MUSIC to only sell the music for a few years, but I wonder why it's only a few specific ones they're pulling.
I just poked around a bit and it appears that the
Gradius II NES album was already pulled at some point in the past.
EDIT: Actually looking into it further, it seems like that's exactly the case: I've found some news notices for some digital albums and all of them are being pulled after exactly three years of distribution. The physical ones being stopped were also released around the same time as those.