What attracts you to Late Rome?

[Flavivs Aetivs]

I'll answer anyway. :-)

The people were still there, but the constituency (or support for the empire) was gone.

The interesting question about the late empire is, when did this process start and why?

It seems to have gradually accelerated after about 300 CE, and peaked in the early-mid fifth century. Part of the problem was that the empire alienated important groups, from the senators, barred from military command, to the barbarian recruits, victimized and alienated in 408.

And why did it not happen in the East?

I think it did, it's just that the East being less subjected to permanent invasion, managed to hold on long enough to regain a good constituency, or citizen support.

That's not true, the Military and Beuracracy was rather closely intertwined. What alienated them was that in the west you had a single generalissmo appointing his supporters, albeit most of the Roman politicians were dumber than a bag of rocks. Aetius wasn't even threatened in his power until he tried to betrothe Gaudentius to Placidia.

Many barbarians did indeed support and want to be part of the empire, the alans under Goa and Sambida were good examples, and so were the Brittones of Armorica who left Britain because wanted to remain a part of the Empire. The Frisians in the 4th Century were loyal citizens after they had fled the destruction of their homeland, its possible they even fought at Chalons (Jordanes records Saxons, which may have been a reference to Frisian LAeti who had been settled in Flanders and Kent throughout the 4th century.)