Yes, it is true that trading is not gambling, and it is wrong to think that it has a similarity to gambling because trading is a skill that can be considered an individual's benefit, so for others it is a course, right?
Indeed. Trading is different, it can't rely on the luck as gambling. Sure, trading requires ability/skills, knowledge is very crucial in trading. If we have no knowledge, it is impossible to have proper ability/skills. There is no chance to take profits without ability/skills. Meanwhile in gambling, we can win it even if we have no ability/skills at all.
Whereas in gambling, you won't hear anything about it being a course; instead, gambling is known as fun and entertainment, and winning really depends on luck, while trading is not like that.
Sure, we don't need certain lesson in gambling. For luck-based games, people can play them without any lesson. You're right, mostly people only spend time to get entertainment in gambling. So, they are not so serious to learn the gambling games specifically.