They do, but the burners are rarely the same as the ones on the superior open burner ranges, so you end up paying as much, or more, for a high-end sealed burner model that doesn't perform as well as the equivalent open burner model. Typically the 'Professonal' model (best performer) from a high-end brand will be open burner, and the 'Designer' model (pretty but lower performer) will be sealed burner.

In actual fact, I find it easier to clean an open burner range because they come with drip/spill pans that can be taken out in two seconds and cleaned by hand or in the dishwasher.

Ultimately the purchase decision should be based on two things, 1) performance and 2) how much you're willing to spend. Open burner ranges are the best, but they are much more expensive than residential grade sealed burner units so it's all about priorities; is performance more important than price?. Clean-up shouldn't be a decision point because it's easy (albeit different) with both types. Sealed burner ranges are a 'marketing creation' to address the 'perception' that open burner ranges are messy and hard to clean, when the reality is they aren't.