Why do you think the Romans gave full citizenship to conquered people living close to Rome?

Rome gave full Roman citizenship to her Italic allies in central and southern Italy because they wanted it. Many of these allies rebelled in what had been called the Social War or the Allied War (90 BC-88 BC). This war broke out after Marcus Livius Drusus, one of the plebeian tribunes for 91 BC, who proposed to grant citizenship to the Italic allies, was assassinated. In 90 BC. Lucius Julius Caesar, one of the consuls for that year passed a law which granted citizenship to the allies who had not revolted. In 89 BC the Lex Plautia Papiria, proposed by the plebeian tribunes Plautus and Papirius, provided that men form allied states could obtain Roman citizenship by registering with the Roman praetor within 60 days of the passing of the law. Whilst the law did not grant citizenship to the allied groups it allowed individuals to obtain it. However, it failed to persuade the rebels to end the war. The new citizens would be placed under new tribes (voting units) instead of being integrated into existing ones. This would have made their votes worthless because the new tribes would have been outnumbered by the older ones. The rebels lost the war.

Full Roman citizenship was extended to all Italic allies after the conquest of Gallia Cisalpina, northern Italy (225 BC-222 BC).

The Italic allies wanted Roman citizenship to gain equality in status and rights with the Romans, the protections guaranteed by Roman law and a say in Roman politics.

The allies had to supply soldiers to fight in auxiliary units which supported the Roman legions at their expenses. They provided some 60% of the military manpower available to Rome and made Rome the biggest military power in the Mediterranean. The system worked because Rome supported the ruling elites and shared the spoils of war (which could be considerable). However, Roman land policy favoured the large landowners and many Italic peasants became impoverished. The Italics wanted greater rights to match their military obligations and to have a say on land policy in their areas.