Do you consider the cost of an unauthorised overdraft when opening a bank account? Do you consider the late payment fee when taking out a loan? Do you consider the cost of foreign transactions when choosing a credit card? Do you consider the cost of ink cartridges when buying a printer?
Maybe you do, but most people don't. People aren't price sensitive to every element equally. I recall the first time I used roaming. I was in Heidelberg, Germany, using a UK-issued SIM. The cost per minute for me to make a call to a local number was over 1 USD per minute, billed in minute increments (i.e. a 10 second call would be billed as a minute).
If I had known that before I left, would that have been enough for me to research other carriers' roaming costs and switch? Probably not.