I checked some information for you, and I also integrated the guesses of my friends. Everyone thinks there are several reasons for this, and no one can say why. I can only let everyone refer to it and laugh it off:

One is related to superstition.

Superstitious people think that there may be goblins and ghosts living in bananas. Because bananas are usually planted in orchards, and goblins live in orchards. You know, the orchard is probably in the middle of nowhere, but people want to eat bananas and are afraid of being possessed by goblins, so superstitious people draw red symbols on bananas to exorcise demons.

Second, as the first floor said, because the place where red paint is painted is often ugly and black.

Third, bananas are planted before they are ripe. Red paint contains some substances that can promote maturity. If you paint a little red pigment on bananas, it will help bananas to ripen early, so people sometimes don't like these because, after all, they contain chemicals.

Fourth, it has something to do with Chaoshan people's apprentices on the first and fifteenth days of the first year. Painting them on them means good luck, just like putting red paper on grapefruit and rice in Yue Bai.

Fifth, farmers mark bananas to distinguish who planted them. It is said that bananas in Zhangzhou were very delicious at that time, so they were painted with red paint to distinguish them from bananas in other places. Over time, it spread to the Chaoshan area, and everyone had to draw like this to prove that their bananas were the best.

Hehe, almost. I hope I can help you.