@hilde45 - I’ve never encountered one in the wild. I have no way of statistically examining a sample of every connection ever made to a speaker. All I can do is talk directly about my experience and I've never had a banana come loose just because.
I can't say that about spades, at all.
I have seen the cords pull out of a banana plug at a dealer, but that was nothing to do with the banana to speaker side, and I'd expect it had more to do with the wear and tear dealers put on their cables while switching demo speakers.