Why can’t barbarian peoples be called civilized? What attracted barbarians to the Roman Empire?

Because they have a low level of culture and development. True, on the other hand, this is a rather biased characterization. The Roman Empire itself at that time, or rather in the 5th century, was very weakened, it was no longer the empire that was supported by numerous legions. The barbarians needed a territory for resettlement. Thus, when the empire collapsed, the barbarians occupied its lands and formed their states there.