There is no technical reason why quicklisp couldn't use the systems libcurl and openssl when its available and fallback to fetching with its portable http implementation when they aren't available.
Every other languages package manager has managed to solve this issue!
If the issue is that nobody has actually had time to work on it, that's fair, but I don't believe that optionally supporting libcurl would cause QL to be less portable.
There is no technical reason why quicklisp couldn't use the systems libcurl and openssl when its available and fallback to fetching with its portable http implementation when they aren't available.
Every other languages package manager has managed to solve this issue!
If the issue is that nobody has actually had time to work on it, that's fair, but I don't believe that optionally supporting libcurl would cause QL to be less portable.