My experience with the Bike Kitchen and AMS Bike Co-op in Vancouver BC is a little out of date, but from what I remember the volume of donations never really abated, but what went down was the *quality* of donations. We used to get a decent amount of 1970s/80s/early 90s bikes where even the low-end models were worth fixing up (steel rims aside). It seems we eventually scoured every garage of those types and started getting late 90s-recent big-box-store brands that are only worth their weight in scrap metal and maybe a few parts for scavenging. No moral judgement on the people buying these is intended, but it's very disappointing to see a Supercycle/Ironhorse/CCM or whatever roll in with absurd "faux-suspension" and triple gearing with steel chainrings.
Jean-François