I get your point, but
1. AFAIK any OS disable bluetooth by default.
That's true most of the Operating System disable default Bluetooth by default but sometimes the users enable it and don't really care much about it because of the short range it has. Some people enable to it connect Bluetooth speakers and headphones and don't really care much about security when it comes to Bluetooth connection and that's can make things easier for hackers.
2. Bluetooth if OP already uninstall all network driver.
The same answer here as well like most people don't really care much about Bluetooth when it comes to security and they may not disable it only to connect some Bluetooth enabled devices.
That doesn't apply for OP though since he has some security awareness and plan to use his PC only to manage his Bitcoin. As for people who don't care about security/bluetooth is likely to be connected to internet all the time anyway.
For instance, do we know which hardware and software are always good sources of entropy and which aren't?
It's easy to know bad entropy source, such as current time. But even source of entropy which usually deemed good/secure can't be always good/reliable. For example,
/dev/urandom output used to be predictable for about a minute on embedded device[1].
[1]
https://www.usenix.org/system/files/conference/usenixsecurity12/sec12-final228.pdf