"Are there no written songs that show these qualities?"
I'm sure there are Vic , but not among the broadsides I'm familiar with
"Are there other factors and facts that appear in folk songs and nowhere else? "
There are features of folk songs that appear everywhere, but there is no other genre I know of that consistently overwhelmingly represents the folk voice and was identified as genuinely their own by the people that sang them

I have yet to see Yorkshire or Lincolnshire variants of 'Bird in a Gilded Cage' or P'ut a Bit of Powder on it Father' or 'She Sits Among the Cabbages and Peas'
When we (you and I) discussed the 'you know a folk song when you hear one' issue ealier on this thread, your response was that instinct was not enough, or words of that efect
Now, it seems, there is nothing about folk songs that set them apart from other songs

If you "need tha details" we are speaking in different tongues
Bert knew the difference when he posed his question; Walter knew the difference when he went through his repertoire ticking off what were folk songs (and why) and what weren't; Mary Delaney knew the difference when she refused to sing us her Country and Western Songs
Mikeen McCarthy was pretty sure he saw pictures when he sang his folk songs and didn't when he sang his parlour songs
Topic Records knew the difference wen they largely confined their output to one type of song and called their monumental series 'The Voice of the People'
So did Gavin Greig, or Hamish Henderson..... or all those who captured, documented and categorised these songs
Even Steve Roud knew the difference one time when he numbered only folk songs and rejected those that weren't
Are you suggesting that all these people didn't know what they were talking about

This anything goes attitude was once a revival thing when the singers ran out of imagination - - now if seems to have spread to the desk jockeys

"yourself to claim that they are the creations of the "common people""
I have always said that nobody knows who made them and said that we probably never shall - that remains my position
It took a while before Steve to punctuate his claims after he had contemptuously dismissed my MacColl's statement as "starry-eyed-nonsense"
Now you are picking me up for having omitted it
Where were you when I Needed you back then?
Sorry - my point and all my unanswered questions remain
Jim