Last time this topic was discussed I saw a very similar question so I had a theory: What if physical card packs is such a small market that government have simply not noticed enough to care to regulate it. I then went and look up the numbers and checked. If I recall right:

Magic the Gathering and Pokemon sat around $500k in realy global market sales. Sport cards a few millions. Game with lootboxes is estimated around a half a billion. Regular gambling estimated around $400 billions.

This make in my view a rather simple answer why Magic the Gathering might not be a big concern for government but why regular gambling really is and why loot boxes currently sit in the middle. To simplify: 1x, 1000x, 1000000x.