If I have to take a stab at it, they are given based on album sales. Below is album sale uptil March 13th
Source for data
Note:
- You can see the cut off at getting a sololive is SorAZ recently getting one on January this year. Pekora was a special case because they are very confident they can sell out a Pekora concert.
- While oricon doesn't count kaigai sales, the western world has largely moved on from buying albums and stream shit on spotify instead so I don't expect much increase for Irys/Baelz, except for Mori who even topped Billboard charts.
- Marine has no sololive due to not releasing an album and seems more interested in blowing all her money into MVs and her 3D lives.
- 5th gen isn't up here but Blue Clapper end up being Holo's no.4 most ever sold single and Nenenenene somehow is around top 10 as well, so Holo was confident in giving them a live concert.
@Nenélove's oshi is hard carrying the gen when it comes to music.
- Kiara/Irys/Baelz album sold so shit Hololive doesn't want to take a gamble for a sololive with big venue. They needed to pander to the Japanese harder.
Unrelated: I didn't realize how much of a monster kanae and kuzuha are, they easily lapped suisei in sales.