If you’ve ever visited my islands, you’d see that I like to have as many habitats and dragons in them as possible, even if they are full of easily reproduced dragons like Primal and Pure and Kratus. One of my biggest ongoing goals is capital investment - increasing potential capacity as much as possible. So I have all islands, 200 habitats (and more waiting in storage), 2 maxed rainbow habitats, 6 kindergartens (which may be replaced over time with rainbow or other habitats like them, pending space), and all 800 dragonarium slots free.
One thing I care less about is decor and aesthetics. I’ve tried to do something with it before, but with so much on my islands, it is tough to make it look nice, and I’m not good at it.
So I opt for practicality and master points, and the rainbow habitats fit in with that goal beautifully.