Rome fell for a variety of tangible reasons but the greatest reason it fell was that the Roman people were no longer enamored of their own empire. It had become endemically corrupt and the people who bore the brunt of abuse were the people at the lowest rungs of society. Those people were the slaves, the farmworkers, the craftsmen, the artisans, and etc. They were heavily taxed while their rulers employed schemes and artifices (or bribes) to avoid taxation.
People lost faith in the idea of Rome. From there it was a fait accompli that Rome would fail.
No doubt at the end there were brave individuals who fought to preserve the Empire but even they eventually gave up or died.
It was opposite. Elite never imagined it would fail and barbarians wanted to become Romans since it was always so
Late Empire wasn't able to integrate Romans due to lack of money. Previous path was recruitment in auxilia with 20 years of paid service to learn Latin and culture. Without money barbarians stayed under control of their kings inside Roman borders.
And barbarians learned organisation from Rome, so threat wasn't anymore chieftain with tribe, but king with tribal confederacy. Far more dangerous opponent. In East situation got worse where Parthians got replaced with Sassanins, true peer to Rome.
Additional reason is 100x of imperial bureaucracy. Diocletians has 35000 bureacrats, while same number at start of 200s was 300. So taxes had to up to pay for all these people (and for larger, more expensive, less effective) army. Result was total crushing of economy. Instead of army being payed in money, army had to go to collect grain which implies that Meditterean- wide trade network has collapsed. So fall in production crashes living standard which get hits again by ever larger taxes.
And don't forget that bureaucracy will create more and more laws to fix problems created by overabudance of laws. So again crushing economy. Don't forget that in such situation path to wealth isn't throught market anymore, but throught political means. Bribery, new laws, army.
This was all only payable throught dilution of metal content in money. We call that today money printing will all joys then as now.
So population runned to barbarians because there were no/low taxes. Or they stopped being free men and become coloni under protection of rich landowner who was powerful enough to have no/reduced taxes. Think how powerful you had to be to run away taxmen.
This has all resulted in massive wealth inequality in order of magnitude of elite being 10,000 times (not a typo) richer than regular population. This people could easily become independent and raise army to defend themselved, but didn't. They too believed in Rome.
Result was massive social instability. In Early Republic, it was more like confederacy of 1000s cities. Each city run itself, with very light taxes for army and foreign policy under Rome's preemience. Now all local distinction and indepedence were getting destroyed. So local politics wasn't important anymore, while imperial policy got more important. Which made getting in favor with emperor more important which raised stakes in fight and made fights more vicious. Now it was truly fight for life or death.
Emporers tried to unify empire using religion which resulted in first pagans prisecuting Christians, then opposite. Emperors throught if all people shared religion infighting will stop. Well, they did opposite. And true reason was all infigting was destruction of any local independence.
Belief in Rome was too powerful even after it died. Justinian tried to restore it. And even when rulers couldn't do anything, they still copied bureaucracy aspect with same end result. Crushing economy results in whole system collapsing and getting more localised.
Best what Roman Empire did was it died. And I hope that idea of powerful empire finally dies.
West had become what is was thanks to being unable to centralize itself ever again. Otherwise we would finish as Chinese. Powerful advances forward stopped by eunuch in imperial palace.