[kindly]

I currently use a sha hash (with salt) but rehash it x amounts of times. I have changed x over the years to be larger to get an acceptable trade off in computation time. Why is bcrypt much better than this? Is it because the algorithm is less gpu friendly?

[Xk]

What you describe is basically PBKDF1. If you wanted to make it slightly better, you could go with PBKDF2. It's true that bcrypt is better in some ways, but you're fine with what you're doing now. If you really wanted to improve on things you could go with scrypt which eats memory also, but it's more difficult to get things to work right.