Are you a lawyer? Why do you only ask questions to which you already know the answer?

Snark aside in case you're seriously asking, it's a PR thing. Generation to generation might not show much differences in direct comparisons that makes the crowd ooh and ahh. The M1 chip was the first Apple Silicone chip, so going back to their first one for basis of comparison provides for more oohs and ahhs. The charts look pretty this way too.

For people who upgrade annually, comparisons don’t matter.

For people who are making a forced purchase, comparisons don’t matter.

For people who are content with what they’ve got, comparing with the oldest-popular market segment offers a clear statement of improvement and helps long-term users calibrate when to make their next purchase.

Guess they have usage statistics to know a lot of their users are still on M1.

My partner and I are both still on M1 (our personal machines) and don’t really see the need to upgrade.

Well, in this case it's totally relevant as the extant studios are all M1. They never got M2 or M3.

M2 Mac Studios were released in June 2023. https://support.apple.com/en-us/111835