I imagine things like this is a result of the account management part of LinkedIn being built years ago when we thought plain-jane sha1 was ok to use, and then they just never got around to using bcrypt.
Ironically, the algorithm to upgrade to bcrypt is simple. Add a flag to the account table if they've upgraded or not. Next time the user signs in successfully, re-hash their password with bcrypt, toggle the flag, and update the password_hash value in the database.
Ironically, the algorithm to upgrade to bcrypt is simple. Add a flag to the account table if they've upgraded or not. Next time the user signs in successfully, re-hash their password with bcrypt, toggle the flag, and update the password_hash value in the database.