Comment by prognu

Simple. Give the manufacturers the choice: either they must provide full (FLOSS) source code and documentation (full schematics) to the user to enable them to maintain, patch and thus secure their devices (see also: right to repair), OR they are liable for all damages (direct, indirect) for a 30 year expected lifetime that arise from security issues with the device AND must have insurance to cover those damages (so that they cannot get out of that liability by bankruptcy). Most will opt for FLOSS, and none will have the excuse that it would be more secure to make it proprietary. And then users will at least be able to fix issues -- and the security community will be way more effective at finding issues as it wouldn't have to do the slow reverse engineering.