It’s a good thing some of you don’t run companies. 
Battlegrounds is a mode designed for getting attention. It is practically built for streaming, Twitch, and other events that people queue up for on the internets. And it does what it’s supposed to do … it gets eyeballs.
Hearthstone Standard was not getting eyeballs anymore. It’s streaming numbers were down. Along comes Battlegrounds. Suddenly the eyeballs are back. Go figure.
So no - you’ve got it exactly 100% wrong. They aren’t charging more for HS so BGs are free. BGs are free to bring more streaming revenue to Hearthstone. Not everything is about you.