The problem with the "cleaning ani" is that if it took up too much time (extended duration VS standard trashpick duration), and froze the player for too long, it would allow other players to take advantage of that and kill them more esily, as trash is typically found in the overworld, and sometimes in non-player-killing-protected levels. This would offer a disadvantage compared to the otherwise standard/offered trashpick.
As far as the lack of vacuum sound during the current usage-ani, I can't speak as to whether it was an oversight or not, but I share your concern when it comes to having a vacuum sound play when used and not just during the special...