Presumably your users don't want to wait 6 minutes to log in, and nor do you want to tie up a full core for 6 minutes running the hash. That's the problem with increasing bcrypt's work factor - you have to deal with the increased difficulty too.

If you're doing salting properly (a unique CSPRNG-generated salt for every user) then 3600 attempts per hour really isn't enough to get anything except the lowest of low-hanging fruit.