It's really a culture. People smoke cannabis to feel part of a clan or a cult, and then get hooked to the psychoactive effects.
It's always a game of social influence at the beginning, and sometimes later on.
Eventually, you may be pushed to smoke if you want to feel part of a social group and culture, and then, once inside, you have to follow the codes of it.
A large part of the cannabis cult(ure) is to preach the substance to everybody around you, to get it depenalized, legalized, and want everybody to have good views on it so they can take it more in public, and be socially more accepted, not considered like a junkie.
The end-game of it, is to do everything to get more of it, consciously or not.
Then, from that perspective, now you have someone that asks you: "is cannabis good for you ?" (just in other words).
Your goal to consume cheaper and higher quality of the substance, without legal risks, and to have approval of your friends, then what do you say ?
Of course "yes it's great".
There is also a survivorship bias in the study: once you feel that your cognitive abilities decline, you typically stop smoking cannabis.
The extreme case: people with dementia are automatically excluded because they cannot even smoke or purchase the product.