Since it has been a long time, so I won't reply to the comment that mentioned it but I forgot if the manga mentioned it, but in the webnovel, the discovery that monster cards awaken with dropping blood on them was found when some people manage to awaken it during the Angolmois, so while it wasn't mentioned, I could imagine those people who awakened them got attacked by monsters and got the cards all bloody and just went to rely on the mysterious card that they don't know what it does to save them out of sheer desperation.
As for the being sociable, well like one of the other commenters said, it is likely that it's not like no one did the same, it's just that the particular cards he has haven't met that kind of adventurers before. And just imagine this, even if it is widely known you could improve them like that, are you sure there won't still be quite a few who would still treat them harshly? Things would work better if people is willing to work together with even their fellow human, doesn't change how there will always be some people who would rather antagonize everyone or expect their every word to be obeyed and refuse to listen to others opinion.