I won't ride in the rain, unless it's a commute, and it's light enough that it won't soak through khakis in a half hour.
Riding is fun. Riding in rain is not fun, so I don't do it. If it's not fun, then the only reason I would be on my bike outside is for training, and I've got a smart trainer in my dry basement now...so that eliminates riding purely for training outside.
Riding with a THREAT of rain is a bit of a more interesting question. If there are expected thunderstorms, but it's currently dry..do you ride? Do you shorten your ride? This is what keeps me up at night