Because it was early middle ages - that why. Plus Kiev was ruled by Scandinavians up to 1050.
Where was Poland as a country in 1800-1918?
Answer to that is complex. Short one - yes. In one form or other. A different angle - at least there was a country - continuous for the most of the history with short discontent.
In Ukrainian it is opposite. Hell even countries like Burgundy or few others have more evidence and history stacked in their favor. Those claim to Kiev Rus are a stretch, not language nor a culture nor political structure of Ukraine has anything to do with it. Hell not even religion, Orthodoxy of Ukraine (fragmented) is not Orthodoxly of Kiev Rus and has been shaped by its history.
Like there three region with different view on history, different languages and we could go on.... there is mothing that could be counted as count unity in anyway and there is not even tat much in common.
Hey do I say anything. It is possible for people bunched on the same territory to say - hey we are not Russian we are not Poles or Moldavian and we are not Kazakhs - we are Ukrainians and aspire for their own country and build some myths to support that claims for nationhood. I don't disparage that.
However I have no patience for some bizarre claims. Talking about territory. The only reason Ukraine has that territory is because it belonged to Soviet Union which fragmented.
There is nothing in it borders that reflect history or an actual state of the nation of Ukraine.
A short spell of discontinuity in Poland's statehood doesn't erase continuity across the spectrum and a long history to back it up. There is no free lunch. Myths are not a bad thing but if you have nothing but myths it doesn't bode well for the people or a country.
Poland is forced to permit Ukrainians to enter Poland to do some dirty job because of its own population decline.
It has nothing to do with that. It just the way current economical policies of the west roll. It is slowly going to change.
Not all the Roman Catholics were ethnic Polish
Nor all Orthodox were ethnic Ukrainians. You can't pick and choose an answer that suit you, it is not a buffet.
Same with statistic IF Polish statistic are biased than Austrian statics are biased too. Also no go into this ethnic thing. Not educated people could be Ukrainians but the same person after geeing an education calls himself a Pole, Divide run into families with one brother saying Polish other Ukrainian. It is much more complex that you want it to be. Besides demographic is only a one of many arguments in debating territory, not that terribly important.