Rollers can have your boat off-centered and off balanced. Rollers will corrode over time and stop rolling especially in salt. Rollers can cause mishap if some knucklehead tries to 'help' by undoing the winch hook too early.

I have a deep-vee fiberglass. My trailer has bunks with dual rollers in the middle for the tip of the Vee. I've had to replace the rollers twice for corrosion or just simple failure. The bunks are still good to go. No moving parts, see?

Rollers you cant run your boat onto the trailer and expect it to be centered.