Word with a similar meaning to "piled together"

Coalesced seems good to me. If you want a negative connotation, snowballed is usually negative. Festered has a different meaning but still fits the context well. Amassed is most likely the word you were thinking of, but to use it you would need to restructure the sentence.

https://www.merriam-webster.com/dictionary/agglomerate

IMHO, you're looking for 'agglomerated'. Conglomerate is a more uniform mix, whereas agglomerate is more irregular, less homogenous, still accretive, but far less orderly. Seems to represent people more closely.

In Geologic terms, anyway. Hope this helps.