So many immigrants from the provinces had come to the Italian penninsula and to Rome itself by the middle of the first century A.D. that historians have estimated that 60-70% of the population in those areas were of non-native origination by the biginning of the 2nd Cent. A.D.
That means that the culture had changed.
Remember, the Roman Empire had no public education that might have enculturated immigrant children to Roman life. As it were, home teaching was the norm if taught at all.
I suspect resistance was low because the invaders weren't all that different from the people living in Rome in the 3rd century A.D.
We have a public education system that does not teach the kids how to be Americans. Same difference.....
Interesting data, good of you to post it.
The principal engines of acculturation were the public religion and holidays, and the public spectacles, which formally speaking were religious solemnities. Every Roman theater and amphitheater had its shrine of Magna Mater/Ceres/Demeter. In fact, after the Roman Curia was burned by the mob during the funeral of Publius Clodius the demagogue, the Senate frequently met in theaters as well as temples; and it was indeed meeting in the Temple of Pompey when Caesar was assassinated; it was recorded that he fell close to the pedestal carrying the bust of Pompey himself -- an ironic touch.
Most of the discussions of Roman decline mention barbarian irruptions, but these weren't significant until after the period you're talking about. The real engines of Roman decline were enumerated by Gibbon, and more recently by Michael Grant. Impoverishment of the middle class by taxation (aggravated by successful cost-shifting strategies used by the senatorial class), depopulation due to plague and contagion, and long-term balance-of-trade deficits with India and the East were more significant factors.