Soft 404
Rumour has it that a lot of i2c slave devices have 8051 silicon in them, that runs the i2c client state machine.
The 8051 takes little silicon space. Most manufacturers already have their i2c client state machine code ready and optimised, only to adapt it to the particular IC and burn it into OTP memory. And no more patents/licenses to pay.
Good call. I note that Silicon Labs offer a dev board which costs about the same as a Pico...