I know this is an old thread, but cannot help commenting. Sorry for the verbosity.
Generally, it is a western US phenomenon. A few things:
1) They fruit COPIOUSLY in Western burns... it is hard to compare to smaller fruitings in the east after you have experienced the West. I don't want to sound snarky, but, usually people who compare haven't actually experienced the Western version. We take a vacation every year in the West and pick burns, from CO, AZ, NM to CA, OR, WA to MT and ID. In all fairness, I have not picked in many states in the East. But, I know that Eastern people that pick large numbers have three things in common, that are not true for burn morels; 1) they have a short season 2) they pick one species/flush 3) they are super in-the-know and have spots. The Western burn morel is easy for beginners to find, it fruits for months, and commonly shows at least 4 species.
2) "disturbance" morels definitely fruit in eastern burns - but likely not in the same sheer numbers. From my studies, eastern burn morels favor Pine forests.
3) Burn Morels are specific species (there are several, and they fruit in succession) and they are rarely known to have fruit in the East: there are 4 known instance, and maybe a fifth will be added from a burn in Northern Minnesota that was hunted in 2022. A DNA sequence is required (Scientists want to sequence your eastern "burn morels"!). I have shared my findings at Understanding Burn Morels if you are keen to know more. Burn morels are picked in Western states from March thru September. May - July are the top months generally.
4) The most iconic burn morel is a Morchella tomentosa. That species has never been found east of the Rockies to my knowledge. But, they do find burn morels in the Black Hills in SD.
Also, just as an aside, people often poo-poo the taste of burn morels. And rightfully so! They can taste a bit ashy, which isn't pleasant. I think that is a function of who picked them and how they picked them. As someone chasing yummy edibles, I avoid ashy morels. I pick clean. We brush clean them before putting in the basket. We use a bag with a mesh bottom not a 5 gallon bucket. Commercial pickers don't care about picking dirty and those morels you buy in the store may have came from someone using a 5 gallon bucket picking in ash. Wait, let me be honest: I pick dirty too! But, I give those away
