[Quoth]

Often T&C by sellers contravene local laws. When that's the case either the clause or entire supposed contract is invalid.

The publisher or author owns the copyright. There have been court cases regarding purchase of software that was later transferred (no copies kept) and sellers/publishers have lost. An book purchase or music purchase in digital format ought not to have less rights for a consumer than the physical copy. Of course some Governments are in the pockets of big Corporations.

In reality, if you don't give copies to someone else (a civil or criminal offence everywhere for anything copyright), then if you bought it they'd have to sue your heir if they inherited legally purchased digital format material to stop them consuming it. Likely they'd lose and why would they waste the money suing in the first place?

Such T&C are probably only valid for library/subscription/streaming, not per item purchases.