Also because Dropbox's EULA almost certainly has a provision that deleting files doesn't necessarily mean Dropbox erases the data right away, just that they won't make it available for recovery and it might be deleted at some future point.
They say "there might be some latency in deleting this information from our servers and back-up storage". But as a user, I expect this to be a reasonable period of a couple of weeks, not months.
