I bet the first guy that did it - HAD to. He prolly lined up his door cutout over a bunch of old attachment points from old pipes/brackets etc…. The cutout was so ugly (and possibly sprung too) that he figured he could build a new flat door easier than trying to salvage the old tank side. It does make a sharp looking tank and anything straight is easier to work with and seal than something curved if it's trying to fight you for sure.
Call me a pragmatist but IT COULD HAVE HAPPENED THAT WAY…..
And on the eighth day God created barbecue …. because he DOES love us and he wants us to be happy.
Current smokers: Egor (trailered RF) and Easybake (tabletop pellet drive)
I agree with Rick that the first guy to do this was to correct problems with the cut out door. If you've never had to deal with a sprung door, you will at some point if you make a cooker out of a tank or pipe. These problems can be frustrating to say the least.
I think it also offers a different look than the traditional tank cooker.
some of the best features on smokers were born because of a screw up.....
anyway to answer your second question, there are goods and bads. you mentioned the whole hog thing already but the bads would be depending on the layout you can't open one door without opening the other or if it is a one piece door you hafta open the whole thing. there are work arounds tho like hinge the center chunk....
Flat doors also offer; no lifting to open, easy locking to prevent tampering, more rack space, it would be easy enough to make the whole thing open too. I think for the whole hog thing.
Current Smokers: Backyard RF Offset and Hybrid RF Offset trailer rig with Cowboy cooker and fish fryer, always room for more........