As a devout Baptist minister, this is likely about one of two things, avoiding the appearance of evil (gambling, 1 Thess 5:22 - Abstain from every form of evil), and giving up something for the sake of others (gambling addictions within the church, Rom 4:21 - or do anything that causes your brother to stumble).
The reality is that most churches recognize that they were too legalistic in the past, and so now address things like gambling more directly, and are perfectly ok with playing cards. FWIW YMMV :-)
I was under the impression that the injunction against playing cards was because of their proximity to tarot/occult practices. Mormons had the same injunction against playing cards until the 80s, when the teaching was no longer promulgated. Speaking as a former Mormon...
Here in Sweden, where we also have free churches such as Baptists, Laestadians etc., the concern was definitely about gambling.
I think that's not wrong. Same principle, different sin... it looks like gambling, or the occult, or...