Developers put in charge of BDSP. Before Pokémon, their work was all extremely minor support for much bigger studios. So for example, if you're a big AAA studio and you want to save on precious development time, you might contract out a dozen studios to do busywork, and one of those studios might be ILCA. For example, two people from ILCA are credited in Yakuza 0, but this is as "Casting Cooperation". Their most major game they'd actually worked on themselves before this was Pokémon Home.

So essentially, you're taking a small company where 95% of their existing work is as a supporting role to do relatively easy work for other major studios, and the other 5% is Pokémon Home, and you're telling them "Okay, now remake Diamond and Pearl."