I don't mean this to sound rude, though I know it will, but this is the literal definition of "argument from ignorance."

You don't use more than two burners, so you don't know why a stove needs more than two.

I personally frequently cook with three or all four burners. Further, there are meals where I might use the two small back burners, and meals where I might use the two large front ones.

I guess you could be describing a need for stoves that came with just two burners, for those who couldn't imagine using more. But, seriously, would you have bought a two-burner model if it had been available, knowing that you might have wished for more even one night a year?

Aor of Indian households when preparing a traditional lunch will have 5-6 items (in the south, particularly in a Brahmin household, you will have one sambhar, one rasam, three vegetable currys, rice, and a fried item usually appalam). This entire meal takes three hours or so to prepare from scratch on my stove (a three burner lpg stove). Two more usable burners will cut this down to about 2 hours

The practical reason is that people have different sized pots and pans. I don't want to put my small sauce pan on a large burner that will waste the majority of its heating surface. Similarly, I need a large surface to heat a big pan.

The aesthetic is that a lot of cooktops are combination stove/oven and thus have to be big enough for the oven bit. Once you already have that surface area, you might as well fill it up to make it seem more substantial. A stovetop with room for 4/5 burners will look like the manufacturer skimped out if it has only 2 burners.