Item Drop Algorithm?

[b4gle]

Hello everyone, new here, I've been searching for an answer to this question but haven't been able to find anything online so I came here hoping someone might have an answer.

I noticed that items in Smash Ultimate follow a certain algorithm, such as the Boss Galga item only appearing when there are 3+ players in a game, and each item having a different drop rate %.
While keeping the item switch setting to exclusively Dragoon Parts and Daybreak Parts (the 3 piece weapon items) they don't seem to ever appear. This seems to be the same with any number of players in a match. I tried including a few other items, such as food and tomatoes, but still, these items do not appear. Are there certain requirements that must be met before an item will appear in a match? And what are these requirements? It seems Dragoon Parts and Daybreak Parts only appear when all the items are included on a big map with 4+ players, but I haven't experimented enough to be sure. There doesn't seem to be any information about what algorithm the item switch is following.

Anyone have any info on this?