Why are international calls from US so expensive?

Wow, just got a $99 bill from T-Mobile for two call to Ireland.  I've been to Ireland multiple times in the last few months as my mother faded away and was used to the $0.25 per minutes rates to call home when I was abroad.  I assumed, stupidly, that the same rates applied calling Ireland from here when I got home.  No - $3 per minute!!!!!  And where is this posted?  Good luck finding that rate -- the link to the rates page is on their international page as a grey text link hidden in a paragraph in a section advertising an additional International service.  

Can anyone explain how the rate is $0.25 in one direction and $3 in the opposite direction?

I usually make my calls on what app, but by mother's sister is over 80 and doesn't use social media.  Guess when I want to call her I'll have top buy their International calling pass at $15 per month to avoid crazy billing amounts.