Security upgrades are never opt-in, and for good reason. The status quo would remain in-secure. Every encryption suite upgrade, SSL software version, DNS versions, etc. maintained backwards compatibility for a window then closed it... just like we have seen here with manifest v2 -> v3.

"Please stop looking at all network requests, especially when you don't need to."

doesn't result in action... while:

"You can no longer look at all network requests" requires extension makers to update to the new paradigm.