When you publicize a vulnerability you know someone doesn't have the capacity to fix according to the requested timeline, you are simultaneously increasing the visibility of the vulnerability and name-calling the maintainers. All of this increases the pressure on the maintainers, and it's fair to call that a "demand" (quotes-included). Note that we are talking about humans who will only have their motivation dwindle: it's easy to say that they should be thick-skinned and ignore issues they can't objectively fix in a timely manner, but it's demoralizing to be called out like that when everyone knows you can't do it, and you are generally doing your best.

It's similar to someone cooking a meal for you, and you go on and complain about every little thing that could have been better instead of at least saying "thank you"!

Here, Google is doing the responsible work of reporting vulnerabilities. But any company productizing ffmpeg usage (Google included) should sponsor a security team to resolve issues in high profile projects like these too.

Sure, the problem is that Google is a behemoth and their internal org structure does not cater to this scenario, but this is what the complaint is about: make your internal teams do the right thing by both reporting, but also helping fix the issue with hands-on work. Who'd argue against halving their vulnerability finding budget and using the other half to fund a security team that fixes highest priority vulnerabilities instead?