Whole turkey is big, awkward, and not flavorful by itself. Not everyone has the time or equipment to give it the care and attention it needs. Frying is popular because it's more efficient heating of the meat on the whole bird. It's the most awkward technique but produces pretty decent results and is its own spectacle if you can hang outside in late November. All-in-all, frying is pretty decent compared whole in most ovens.
But not all ovens. I digress.
Spatchcock solves many of those issues by cracking open the "cylinder" and letting heat more evenly cook the meat. Smoking first taught me to cook to temp/done and I think some butchering produces significant gains in this department. Further butchering into parts is more work but even less risk for at least the same reward, if not more. Cook 'each part until it's done and you get a better distribution of results across the whole bird. Plus, the carcass is now available for making stock in advance. Turkey stock makes better turkey gravy than not turkey stock. Better turkey gravy makes better turkey dinner because it goes on the potatoes, turnip, etc. Deboning is the logical extension of more butchering, but I think provides only very limited improvements for the added work.
Whole turkey is about sentiment, I think. If you're carving at the table, it makes sense that whole turkey adds to the spectacle. We've always carved in the kitchen but we usually had crowds to feed.