Velveeta isn't actually cheese. It's "Pasteurized Recipe Cheese Product". It doesn't contain cheese, but does have milk solids, etc. Because of that, it melts beautifully, unlike real cheese, which separates into fat & solids when too much heat is applied.
I've made my own melting cheese (made with real cheese) using the process in Modernist Cuisine. The method is basically melting real cheese in a bit of additional liquid and adding sodium citrate. You can firm it up in a block (like Velveeta) or in flat squares (like that other fake product - American slices). My homemade 'melty cheese' was a vast improvement in taste, and made a perfect mac & cheese, but for my purposes, too much work for a limited use. If I want cheese to melt, I skip the cheddar and use something that will melt nicely.
All that aside, I grew up on the stuff. Velveeta and American slices were pretty much all my mother ever bought. To me, a bowl of Campbell's cream of tomato soup and a grilled cheese sandwich made with Velveeta was the ultimate comfort food.
A couple years ago when I had a bad case of the flu, I was remembering that to a friend. She went shopping and brought the white bread, margarine, Velveeta & soup and made my lunch. WOW! It sure knocked that memory out of my head forever! Worst tasting c**p I've ever eaten!