[juancb]

Because there's a computer in your mouse and you need software on your host computer to talk to and peogram the mouse's computer.

That of course would make it optional like with most programmable keyboards but then there's the need to manage pairing via their wireless dongles and then it quickly becomes necessary.

Outside of it all being intentionally proprietary I don't see why they couldn't take an approach similar to VIA in managing their devices. There's also prior work for flashing microcontrollers from the web browser, I'm thinking of ESP32s specifically.

https://www.caniusevia.com/

[brokenmachine]

Logitech devices are probably based on old code from older devices before WebUSB was a thing.