The problem lies in that the builders and insulation contractors or any other contractor for that matter essentially do not talk to each other. That is the cause for hot rooms, poor airflow, unless art heat gain into your home and high utility bills but I digress. The lack of communication and just poor practices or laziness on part of insulation contractors is the reason why baffles or ridge vents are not placed at all the bird vents above the house.
But why are they even needed in the first place? The reason is two-fold.
1. Baffles direct airlflow up the roof slope and out the ridge vents if you have them. If you don't have baffles then the air that vents the attic will blow back the insulation a good foot or more from the sides of the house.
2. Some contractors will put a fiberglass batt in-place of a baffle because the fiberglass batt is rigid and won't blow back. The fiberglass batt insulation will allow airlflow to pass through it (as all loose fill insulation will) but there is a problem with this scenario. The fiberglass batt insulation allows hot outside air to pass through it but it does not direct the airflow up and away from the drywall ceiling. So while the outside air is passing through the batt, it is also heating the drywall which defeats the purpose of the fiberglass batt.
Baffles can be cardboard, plastic or Styrofoam material and come in 16" on center or 24" on center sizes. Expect to pay a little more for baffles especially in a retrofit situation and garages are NOT included in the square footage of your attic or in insulation quotes.