Duos in Battlefield 5’s battle royale “Firestorm” mode has been officially removed by DICE. In a Reddit thread, originally reported by VG24/7, DICE community manager Freeman explained that the mode failed to consistently draw enough players, who instead preferred solos or squads.
Duos was originally launched as a limited time mode in April, and was subsequently removed not long after. According to Freeman, enough players voiced their interest in duos mode for DICE to implement it as a permanent mode.
Source: IGN.com Battlefield 5's Firestorm is Losing Duos Mode Due to Lack of Interest