Why have cards gone to gem purchases only?

I used to be able to buy cards with coinage.
Now it’s changed to gems, why??
And cards are now proportional more expensive as gems are much harder to come guy.

That means coinage is now only uses for leveling up heroes and some challenges??

Scroll all the way down. The chests are current at the bottom of the store, and the 5-hour rotation of cards is right above them.

Ummm they haven’t? At least not for me. Whether they are coin or gem seems to be random to me. I have seen all coin or coin and one or two with gems. Maybe you just got randomly cut with an all gem one. Wait until the time is over and see if it switches