Why did Allah describe disbelievers as unjust in Surat Al-Baqarah ("And the disbelievers - they are the unjust"), while He described hypocrites as defiantly disobedient in Surat At-Tawbah ("Indeed, the hypocrites - they are the defiantly disobedient")?

The two verses mentioned contain exclusivity. Disbelievers are the wrongdoers and none else, and hypocrites are the defiantly disobedient (fasiqoon) and none else. Wrongdoing (dhulm) is associating partners with Allah, and for this reason, absolute wrongdoing is confined to disbelievers, because they deviated from that for which Allah created them and associated partners with Him. Disobedience (fisq) is deviating from religion and obedience, which is a characteristic of hypocrites. Therefore, they alone deserved to have disobedience confined to them due to their deviation from obedience and their stripping away of all good.