Eh, maybe, maybe not. What guarantees are there that the backups actually get deleted? Storage is cheap these days...
There's no business case for keeping backups around for Apple, unless they suddenly became an ad company and started mining your backups for personalization data.
For the longest time Facebook couldn't actually delete photos that you requested the deletion of. They could remove it from indexes so it couldn't be found, but if you had the link it would still be available (akamai cdn). Because, to them, either the cost of the hosting was miniscule compared to the cost of writing the software to ensure things actually got purged from the CDN.
Outside the EU, small companies, or non-tech companies might we'll keep it forever.