It's because gambling is for fun, which is why people got addicted to it as a form of entertainment, but in trading, it is somewhat of a skill or a job that you are pushing yourself to do just to gain profit. Also, people really misconstrue trading as gambling, as others just treat it like gambling by guessing where the price goes and relying on luck, and that is where the big losses start. Though there are still people who are addicted to gambling, let's say their screen time is more than 8 hours, as they are really wanting to trade, which is also a bad thing because you'll be trading huge amounts at that time and again prone to losses.
Trading should not be taken as a job, although it can be a job for those that understand it. Trading can be worse than gambling for some people, they will learn but still lacks the knowledge to make profit with it. For anyone that is trading, it is good to first use small amount of money and continue with it. In trading, someone can be addicted and continue to trade and lose. I am not disputing what you said, but trading is very risky like gambling.
I think trading could actually be consider as a full time job, cause if a person is doing full time trading and that's where he get his money income to provide all of his needs. Same way in gambling, but I think it would only apply to those professional gambler where they are paid by just gambling since they are being paid for their talent, also consider the paid promotion such as advertisement. But if you are just an average person doing either trading and gambling, then it would be hard to consider it as a job for you since if you're not good enough how you would provide all your needs if you are starting to lose some money in trading or gambling right? So it really dpeends