There is so many things wrong with this.

The biggest one being the cards themselves are a collector's item, they can only be acquired at the 2019 con. Having virtual collectors items is nowhere near as cool and considering that people traveled all over the world to new zeland, virtual cards would be a big let down, since it's not going to be a real game to play outside of the con.

Secondly, one of path of exiles biggest design choices, trade, is much easier with physical cards. The aim of the game was to get people playing in real life and interact with all the staff, not to be on your phones playing path of exile-mon go.

Lastly, pretty much all software has some bugs. If you instead print out cards, GGG saves a lot of headaches from any bug related issues or having to spending time cracking down on bugs.