Same bullshit argument was made about GDPR and we survived that... there's just too much money to be made by outsourcing your shitty code's security bugs onto the customer.
GDPR is basically "you are liable if you are actively exploited and data is stolen". You're saying that a company is liable if they ship bugs, which the GDPR absolutely doesn't care about.
What? No, you have to have a DPO, provide clear language on what you do with data, who it's shared with and no intrusive prompts having opt-in by default just to have a few.
None of those things have to do with the actual security of your code/data storage. They're procedural.
The GDPR focuses on procedural liabilities. You're asking for application level liabilities, which like I've said 3 times now, are a whole different ballgame.
Since you're so deadset on this, I'll just ask again: Who is liable for Heartbleed or for Meltdown? Who gets sued, and for how much, and why?