Because that is very good for bitcoin?
There are a lot of factors to consider. How about the people with no btc? Dollars downfall will create chaos for sure.
World war 3 might happen if dollar will fall.
Dollar will fail; we have to protect ourselves
Protection isn't a simple "Hide my wallet away on a USB and it'll be fine, I'll just tell people I have none." You are looking at protecting entire infrastructure, such as the internet itself. The dollar collapsing will end up with huge power grabs in the chaos that would ensue, possibly, and so things as delicate as the internet would have to be very well protected. And I don't mean the main servers, I mean every other piece related to it, like routers, ISP servers housings, all that stuff.
I'm torn between physical assets and Bitcoin, to be honest. Bitcoin has amazing potential, but if the internet goes down, which has a likely possibility if the dollar would collapse, then it becomes far less valuable. Physical assets will likely often be used and accepted if the internet goes down, but then you'd be missing out on Bitcoin in the event the internet doesn't fall...