You are forgetting that with the subsidized you paid a portion of the phone up front.
The last phone I subsidized cost me $299 out of pocket, plus taxes, and my line on my plan was $40 per month.
When I got my 6S, I paid the $299 up front just like I would have if it was subsidized, plus taxes, then my plan was $20 per month, plus $18.74 for the phone payments. So since you are complaining about people being bad at math, that is $38.74 per month on my line, or $1.26 less per month than with subsidized.
That is because I actually compared “apples to apples” with a proper down payment on the device. If you don’t put down some money up front, yes it’ll cost more per month than it would subsidized, but that is because you have to pay off more than before! You could put down $500 and pay even less per month. It is just a 0% 24 month loan. You can also pay it off early if you want to, but you have to do it as a lump sum.
Tl:dr it costs more per month because you made it cost more per month.