more people may be more active in doing both. but have you ever seen anyone think they are only lucky in one area? Everything can be learned, but sometimes people feel that they are more fortunate in a particular field when they have tried two or more times in doing something.
Likewise with investment or trading. people may be able to do both, but sometimes they always fail in investing and on the contrary always profit in trading. Or maybe on the contrary there are those who always fail in trading but profit in investing. So maybe that's the reason why there are people who don't do both.
There are many things that need to be understood before we start trading or investing. If we don't really understand both of them, it's a good idea for us to choose which area we are good at so that if we do, we don't experience big losses. If we understand these two things, it will certainly benefit us a lot do both of these things.