Thankfully this one's simpler than many folks think and doesn't require that you rasterise the whole PDF at all. It is however, as asked for, a fully destructive workflow: therefore you should save a copy of the file uncropped for use as reference or recovery later.
You crop, exactly as you did, and then you go into the Protections tab, and choose Remove Hidden Information.
Document being cropped
Protections tab: Remove Hidden Information
Remove Hidden Info at work - parses entire document looking for hidden data and dumping it - so for example, with a multi-page PDF you could crop several pages and then remove hidden once and get all the crops completed.
PDF placed into InDesign with Show Import Options checkbox checked: as you can see, crop area only in document at import.
For myself, I'm glad that the inherent and expected behaviour of PDF cropping in acrobat and other PDF viewers is non-destructive, as that is often the tool laypeople use to manipulate the work designers do, and this allows us to "coach" them later in either file recovery or un-doing a crop, and let them know as we ease their panic, that:
a) we don't charge so much that a quick request for a cropped version (or change of resolution or whatever they were trying to achieve) would have been out of place
b) we provide(d) the deliverables for them per the spec in our contract, both file types and resolutions, and perhaps their spec should include xx to account for this heretofore unforeseen cropped-document need... and here, when we're done, I'll just send you a quick change of scope codicil / addendum to our contract, with this recent item as a new deliverable spec, and newly exported fresh from my native files to that spec doc, and I'll bury this support time into the minor fee that the addendum calls for - so either you got this support time for free, or you got a whacking discount on the scope change and file delivery - in either case, you, the client saved money and get a clean file to your new need.
Hope that helps.