Explanation: While we in the modern day marvel at how thoroughly the Romans assimilated people, the fact is that the Romans were more-than-happy to allow provinces under their rule to continue most of their traditional ways of life - so long as they continued to loyally serve the Roman polity!
Romans, for all of their immense arrogance and chauvinism, were also very capable of recognizing superior foreign ways of doing things, and either adapting them themselves, or using the foreigners in such matters. This is something recognized both by the Romans themselves and Greek writers - Roman society, for all of its clamor about tradition and the CORRECT, ROMAN WAY of doing things, was flexible and adaptable in practical matters (and also abstract matters, but don't mention that to the Romans, they'll have a fit over not being as tradition-oriented as they talk themselves up to be).
This varied in form from copying Carthaginian ships, to adopting the Spanish sword (the famous gladius) and Celtic chainmail in their Legions, to Greek philosophy and theology, to Anatolian cults, to Celtic and Germanic clothing. In the other way - the recognition of foreign skills - the Romans used a wide variety of auxiliaries in their armies whom they freely regarded as superior in certain skills to native Roman troops (Numidian, Germanic, Gallic, and Scythian horsemen, Balaeric slingers, Syrian archers, Batavian shock troops) and highly praised the arts and wisdom of foreign cultures - the artisanship of the Gauls, the art of the Greeks, the intellectual pursuits (especially in law and theology) of the near-east.
Rome, extremely cognizant of its origins as a little farming village in the backwoods of Italia which burst onto the scene of the wider, more developed Mediterranean, knew damn well that it was not born the center of civilization which bestowed the achievements of man onto its lessers. It became so!
In the words of the Aeneid, a propaganda piece commissioned by the first Emperor, Augustus, but reflecting pre-existing cultural conceptions in Roman society...
Others will cast more tenderly in bronze
Their breathing figures, I can well believe,
And bring more lifelike portraits out of marble ;
Argue more eloquently, use the pointer
To trace the paths of heaven accurately
And accurately foretell the rising stars.
Roman, remember by your strength to rule
Earth's peoples—for your arts are to be these :
To pacify, impose the rule of law,
To spare the conquered, battle down the proud.