[buffaloKiller]

“I’d be curious to know which 200 years you suppose they could have returned?”

The time I am curious about is from 350/400-600AD.
The Romans were gone/diminished by then and Byzantium (my distinction from ‘Romans’) was not such an oppressive overseer that the Jews could not have reestablished.
Albeit, probably not fully independent but a presence non-the-less (akin to Judea under the Persians circa 450BC).

Whatever organization the Jews had before 75AD/135AD would have been still functional hence my Q as to why they were not motivated to reestablish in Judea at the soonest opportunity.
Byzantium did not engage the Muslims fully until after about 690AD (and that continued for 100+ years thru fall of Damascus, then from 3rd Crusade thru the final assault on Constantinople-1453AD) as the Mussies intentionally avoided the contact except in the closer Arabian peninsula/Persian area.

[BroJoeK]

"The time I am curious about is from 350/400-600AD. The Romans were gone/diminished by then and Byzantium (my distinction from ‘Romans’) was not such an oppressive overseer that the Jews could not have reestablished."

Some points of historical background to keep in mind:

• The Jewish diaspora did not begin with the revolt against Rome in 67 AD, but rather with the Assyrian conquest of Israel in 722 BC.
  
• Estimates of the Roman Empire's Jewish population at the time of Jesus are around 6 million (of the Empire's roughly 100 million total), plus some hundred thousands living outside the Empire, mainly in the area of modern Iraq. Of that total, at the time of Jesus, only one in four Jews lived in the Roman province of Judea.
  
• There was never a time in history when SOME Jews did not live in Israel / Judea / Palestine. And, except where forbidden by law (and one assumes, where such laws were actually enforced), those Jews always had their own leaders and councils.
  
• According to my 2007 "Atlas of Jewish Civilization" (a paperback bargain book):

  "The decline in Jewish influence in the Holy Land was accelerated by the accession of Constantine to the Roman throne....[especially after 325 AD]
  "The Christians, hitherto a persecuted minority, immediately began persecuting those of other religions, particularly the Jews, who at that time were actively encouraging conversions and were thus perceived as competition...
  "Successive restrictive measures were introduced against the Jews. In 415, Orestes, prefect of Alexandria expelled all the Jews, and the patriarchate of Judea (Palestine) was abolished in 418. Synagogues were systematically destroyed and their rebuilding forbidden... In 553, Justinian, the Emperor of the Eastern Empire, even issued an edict forbidding the study of the Mishnah..."

Exactly how hostile life may have been for Jews in Palestine during the period you question is, I think, debatable.

But I'll repeat my main point -- even at the time of Jesus, according to historians, only one in four Jews lived in the Roman province of Judea.

Roughly the same as today...