A raspberry pi seems much less secure than a trezor to me

Like, how does it do HDMI? That's a proprietary version of displayport right? And if it has a general-purpose GPU, don't all of those use proprietary code too?

Most importantly, since the system wasn't designed to hold crypto, there is zero-party accountability. If the raspberry pi manufacturer or their parts manufacturers decide to take your coins and you shoot up an office over it, you just look like a dick because you don't know if the people in that office had anything to do with it. All you know is you used a device for something very risky that it wasn't designed for and it went badly. The manufacturers of trezor have taken responsibility for making a crypto wallet and they have incentive to make sure the device they work on doesn't steal my coins so there's no scenario where my coins disappear and I shoot a trezor employee and instead of a villain I'm a hero to all the other trezor victims.