Maybe hardware Wallets should come with some basic instructions. I don't remember but I think my ledger came with some basic intructions like "don't share your seed with anyone"
But a better warning like " never type your seed in a computer" would be better.
Every Ledger device comes with a "Recovery sheet" for users to record their 24 words on. There are various versions, but all contain something along the following lines:
"These informations are uniquely linked to your wallet and you should be the only one to have access to them."
"Confidential 24 word recovery phrase"
"Store your recovery sheet in a secure place"
"Confidential - do not disclose"
Both the Ledger website set up guide and the Ledger Nano instruction manual state:
"Never ever share your 24-word recovery phrase, in any form, with anyone."
"Never enter your recovery phrase on any device other than your hardware wallet."
"Never take a picture of the 24-word recovery phrase."
In addition, when you initialize your device with Ledger Live, you get the following warnings:
"Carefully secure your 24-word recovery phrase out of sight."
"Make sure you are the sole holder of your recovery phrase."
The warning not to share your seed is on the paperwork that comes with the device, displayed on screen when you use it for the first time, in the instruction manual, and on their website. I'm not sure there is anywhere else they could possibly put it other than inscribing it on the device itself. If people still choose to ignore these instructions and enter their seed on random websites, then the fault lies with them, not with Ledger.