It’s a pain in the ass to try to beam contact information from one smartphone to another. With a business card, you just take it from the other person, stick it in your pocket, and later you can scan it in a few seconds.
Maybe someday somebody will invent a universal smartphone app that’s as reliable and easy as exchanging business cards. Maybe it’s available right now and just hasn’t gotten popular yet. But until then, business cards ftw (as people no longer say on the Internet).