Is there a conspiracy for lvl capped players to ignore materia?

[Jeeqbit]

If that's the case why does SE give away top tier materia like candy in normal 80 dungeons ?

To increase access to the materia and make it more likely they will use it, but as I explained most people are overwhelmed or uninterested by anything beyond just playing and doing the story. A lot of people going through the story don't understand what all the things in their inventory are and whether they are important.