DS, not having checked connections in Cun to and from Bze (if you dont need a layover) RT Iah to Bze $472. Iah - Cun $300. Cun - Bze - Cun (Ive seen post from $198 to $345). Using the lower fare of $198 = $498 V $472, it still aint worth it in time, plane change, layover etc, to me, no matter how they package it.
If your departure airport is Houston, Dallas, Atlanta, Miami and sometimes LA, then it isn't going to be worth it for you.
But from any city where you have a non-stop to Cancun (which are many), then you have the same number plane changes if you fly through cancun or if you fly through one of the others mentioned.
And from many others, you already have two hops to BZE. For example, my folks fly out of Traverse City, MI or Grand Rapids, MI. From those airports, you cannot fly direct to any of the above. So if they fly to Belize, they have 2 hops either way. Why not make one of them in Cancun if it's cheaper?