The "kickback" the broker receives is because a broker must:
1) Sit down with their clients to find out their situation and what product is best for them.
2) Package the file
3) Do all the work behind the scenes with one of the lender's underwriters.

This provides and avenue for banks & lenders to avoid having in house mortgage specialists all-together, or in most cases have fewer of them. Which keeps ~$75-150k off their books per employee.

This is why other lenders offer better rates and products than the big banks is because their bottom line is so much less.

Z55man has it right, going with a bank and breaking term will cost you ten-of-thousdands, the average mortgage term is broken in 38 months, and try not to tell me a CIBC/RBC/BMO "mortgage specialist" won't try to rope you into a 5yr fixed term to beat you up on IRD penalty down the road. We all know they get a bonus too, and they are restricted to only a few products.

A mortgage broker is a 1 stop shop to all the best rates.