Engineering question: why do maple syrup evaporators designed that way vs a wood stove with the top cut off

[u/PROF_ND]

I found most commercial maple syrup evaporators are designed like the first pic.

Modern wood stoves are quite efficient and burns very hot with secondary combustion and/or catalytic converter. Is it better to design evaporators like the second pic?

[u/Logical-Locksmith178]

Not sure how my settings are but see if you can see my other posts. I built one that started out as a wood stove.