According the FT article [0] which the Guardian is secondhandedly reporting from, it's for O-1Bs - the O-1 reserved for "[I]ndividuals with an extraordinary ability in the arts or extraordinary achievement in motion picture or television industry" [1]

Based on the FT article, the reason law firms are doing this is because attribution metrics like followers and revenue are easier to use to show "exceptional ability".

It's the same reason why if YC or any employer wants to sponsor an employee for an O-1A, they tend to use a mix of conference presentations (eg. KubeCon), press releases (eg. TechCrunch articles), and other PR strategies to help build a case for "exceptional talent".

It usually costs around $10k-20k (including legal fees) to make a comprehensive O-1A/B application, and it's basically become what the L1/2 used to be until a decade ago. Meanwhile, L1 has become the new H1B, and H1B has basically morphed into it's own thing.

[0] - https://www.ft.com/content/8816fcec-4148-4cda-be7f-fc59d5bcb...

[1] - https://www.uscis.gov/working-in-the-united-states/temporary...