Because there never were safe web browsers in the first place. The internet is fundamentally flawed and programmers are continously having to invent coping mechanisms to the underlying issue. This will never change.
Just because you can never have absolute safety and security doesn't mean that you should be deliberately introduce more vulnerabilities in a system. It doesn't mtif we're talking about operating systems or the browser itself.
We shouldn't be sacrificing every trade-off indiscriminately out of fear of being left behind in the "AI world".
To make it clear, I am fully against these types of AI tools. At least for as long as we did not solve security issues that come with them. We are really good at shipping bullshit nobody asked for without acknowledging security concerns. Most people out there can not operate a computer. A lot of people still click on obvious scam links they've received per email. Humanity is far from being ready for more complexity and more security related issues.