Your response doesn't give any reasons for not using Fabric other than maybes and what ifs that may or may not apply to anyone including yourself. You might as well say "why in the world would I ever use Fabric, I live in a log cabin and forage for food, it makes no sense!"
Also who said they expect all programmers to switch to Fabric AT ALL let alone over night? It's a choice. They are offering a potential solution for java based systems that can, in their opinion, improve the overall security of the system by embedding secure rule sets into the code itself, something that has not been done as a part of the language before.
And as for his statement about "our defenses improving" it makes perfect sense and it's at the heart of what is wrong with systems today. Security is often treated as a secondary concern until someone breaks in, then it's top of mind and only then is it implemented properly.
It's irresponsible to act as if security is a given. It's also absurd to think that simply because someone is concerned with security that that means they are therefor implementing secure systems or even have the capabilities to do so.
Now, is Fabric good? Who knows, only time will tell.