Probably because once you wrap your code around one SSL stack it's hard to migrate it to another. So you stick to the one you use first. OpenSSL, for instance, isn't just an SSL library... since C has no standardized "stream" functionality, it's a whole big generic streaming library with pluggable modules for various streams and the ability to write your own... once you're stuck to that you can get stuck pretty hard if you don't properly wrap it with abstraction, which C is not, ahhh... let's say it's not really the best at that sort of thing anymore, which is of course partially because every language since C has known that it needs to be better than C at this to even be considered by anybody.