Universal Roman citizenship was enacted after citizenship lost its key privileges

Evidence

by this time the most important privileges of citizenship only applied to the higher of the two citizen classes, the honestiores (Senators, Equites, army officers, etc.), as opposed to the humiliores (everyone else). — Stephen Kershaw, A Brief History of the Roman Empire, 1237

Categorization

• corroborated: 2 independent passages support this claim — Stephen Kershaw, A Brief History of the Roman Empire, 1237
• XREF: connects to: Caracalla extended Roman citizenship to nearly all free imperial inhabitants — Stephen Kershaw, A Brief History of the Roman Empire, 1237; All free men in the Roman Empire were to be given full Roman citizenship — https://en.wikipedia.org/wiki/Constitutio_Antoniniana; Caracalla made all people in his empire Roman citizens mainly to increase tax revenues — Constitutio Antoniniana (citing Cassius Dio, Roman History Bk 78) (+1 more)