A long time ago, the comic book industry (facing criticism over their content destroying our youth, and the prospect of government regulation) chose to regulate itself by creating the "Comics Code Authority".
Decades later, the video game industry (facing criticism over their content destroying our youth, and the prospect of government regulation) chose to regulate itself by creating the "Entertainment Software Association", and created ratings like M for Mature, T for Teen, E for Everyone, etc.
Here, the industry regulating itself isn't practical because of interactions with other types of vehicles, dealing with insurance companies when accidents occur, and a hundred other reasons. My take on this is that rather than being regulated in an inconsistent way across different jurisdictions the e-bike industry decided to be proactive and create regulations that were more predictable and consistent. That's a win for manufacturers who can then sell the same product almost anywhere in the U.S., and a win for consumers who want regulation to be understandable and predictable. It would be a hassle if you bought an e-bike in one state, and then discovered (while travelling, or after moving to a new state) that it wasn't street legal in neighbouring jurisdictions, for example. This helps avoid that.
Regulation is undesirable for people who assemble their own e-bikes and don't want to be constrained by max speeds, max wattages, etc. But as e-bike sales grow, that's a declining part of the market overall, I suspect. And since regulation is likely inevitable, so having it be consistent is a win IMO.
I say that as someone in Canada who *wishes* we had consistent regulations from one province to the next!