Err... because paying it off monthly doesn't make it any cheaper. And it still ends up being a sizeable chunk of your total purchasing power.

No but it gives you you better means to purchase an item you otherwise wouldn’t have if you had to do it upfront. There’s greater purchasing power in buying something over time rather than all at once.

I have no idea how much you're making (and no desire to know), but for the sake of the argument let's say it's $6k a month. Try to extrapolate our reality to your own. Would you go around with a phone that cost $18k? Would you even buy one, monthly installments or not (and then get the next one right after it comes out, like many iPhone users here tend to do)?