Why Bitcoin does not user bcrypt for hashing? I've read that bcrypt is a hashing library that can adapt to Moore's Law and I thought that would be great for the network to adapt in a flexible manner its security to its respective growing computing power.

As far as I know, bitcoin already adapts its mining difficulty to the frequency of block generation, I wonder if some kind of similar automatic protection would be possible to do regarding the security of the hashing algorithm itself.

So, can someone with more knowledge on cryptography clarify this?
Because Bitcoin didn't start out that way, and there is a lot of economic investment tied up in hardware that can only perform SHA256d hashes.