Note to self: do not eat the shiny bacon at Casey’s house.
I was always told that the reason was that with the foil you just let it cool and harden, pull out the foil and toss it in the trash (as was said up-thread).
Without the foil even if you pour most of it into a can or something you still wind up washing a greasy pan in the sink which results in the grease finding its way into the drain. This supposedly causes problems leading to clogged drains and the like.
No real cite, just my understanding.