Or maybe they're just friends because they're all white women trying to become asian. Holo doesn't really need to poach, I'm sure there's already a gazillion talented individuals lining up in the recruiter's DMs.
There may be a ton of people sending in their resumes to Hololive, but a known quality in the realm of vtubing is far more attractive to a company than a potential.
To compare it to the NFL again, it's like how head coaches or coordinators can bounce around the league, despite having many bad seasons under their belt. You'll often see them do a terrible job for several years, get fired, and then immediately hired by another team. Why wouldn't that team just hire someone new? Because those positions require a lot of specific skills that aren't all that common, and aren't all that clear if an individual even has them - until they're actually doing the job for real.
But then, you've hired them, filling a position, and letting it rip for a season. If you're wrong, and they're missing those skills, then shit, you've just fucked the entire season - including fucking over all the other coaches and players on the team. Not good. So teams usually play it safe and pick up someone they
know can work the position, and assume (or hope) that the conditions on
this team will have them play out well. At worst, they'll just suck, but at least they won't tank the entire season themselves.
With vtubers, especially in companies, they need to be good at keeping up dialogue while streaming, thinking on their feet, and just generally being entertaining. They need to be, to an extent, consistent with their stream times, with working with managers, and working with other people. These qualities are not universal in any profession, but most certainly not amongst the asocial awkward menhera dorks that are drawn to vtubing. You could even have someone with a small indie past, but once you plunk them down in a larger audience - with the additional expectation of adhering to a schedule, both streaming and behind-the-scenes company work - they could just freeze up and fold under the pressure. There goes a slot in a gen, along with the upfront investment for the vtuber themselves.
Pomu is a known quality, and she's got some damn good quality. Everyone knows what she can do, and they know her draw. Vtuber agencies know she can work in a company and keep pace with management. Add on her reputation in the scene, and any company would be crazy not to want her. The only question would be if she had reached her potential ceiling. If the agencies think her limit was reached while she was in Nijisanji, well, I
could see Hololive passing on her, maybe. Smaller companies would
love that ceiling, though.
But yeah they probably are just friends and I'm seeing more than there is because speculating is fun.