The OP question is based on two false premises. (1) gains on cards have always been taxable, and (2) cards are not subject to the same preferential 15%-20% capital gains rate as stocks. Collectibles are taxed at up to a 28% rate:
https://www.irs.gov/taxtopics/tc409
In some cases it may be more efficient to form a business and pay marginal income taxes on net profits than to take a capital gains approach to card sales. It all depends on each person's specific financial profile. One thing I am pretty certain of is that no one is moving money from tax-efficient investment like stocks held for more than a year to a less efficient one like cards if they are making decisions based on capital gains taxes. Money is going into hard assets like cards because of two factors: (1) a belief in short-term potential for flipping in and out at a profit that cannot be garnered in other investments, and (2) as a small piece of a portfolio to hedge against inflation, similar to how metals and other tangible assets have been treated in the past. As to the latter, with the high expenses to enter and exit the market, I think it is not a good investment relative to others. But they are fun to own; you can't beat looking the Bambino in the eyes.
