Technology

I think of it more comparing a game like D&D which would work well under an open source model.

A large part of the appeal to a CCG is the interaction of the different cards together. It is a set of cards to play with, not a series of individual cards. Traditional trading card games, living card games, and deck builders are built on these card interactions. Sometimes it involves designing synergistic mechanics but it can just be creating the environment where different strategies can compete against each other. New cards get added in part to fit well with existing ones. Cases this doesn't happen is considered to be a failure.

The open source model does not work well with that design goal.

There is going to be an inducement by designers to push for power creep since designing stronger cards will get them played. There may not be enough headroom for a game to deal with the constant increase in power.

You also have the fracturing of different formats. It took a while for Magic to get to the number of formats it had and even then most constructed play defaulted to Standard. How are you going to be able to have a CCG work with hundreds of formats filled with cards that don't work with each other and can maybe even have homebrew cards that wreck the metagame?

A card game isn't like an RPG where you can have a base rule set while letting others create potentially clashing supplemental sets and adventures. Hell, we've even seen forks like with Pathfinder. There is a reason why RPG's adopted an open source mindset while card games didn't.