A good answer I saw:
Keepers had worn gloves in rain/mud/cold weather almost from the start of the game, but they didn't start wearing them in all conditions, as they do now, until the mid-late 70s. German keeper Sepp Maier is generally credited with starting the trend, and by the 1978 World Cup it was very rare to see a keeper without gloves. By the 1982 World Cup, the modern technology of latex-palmed gloves was established, and every keeper since then has worn them.