Surely "Why are you leaving scissors on the table?" should also be correct. That is certainly very natural English.
But doesn't that mean that there us more than one scissor?
I think I would then say "Why have you left all the scissors on the table?"
yep, I would say either as a native speaker...
"Why are you leaving scissors on the table?" is accepted, and frankly, the Polish sentence doesn't specify whether it's one pair of scissors or ten of them.
True! It's easier when you are in the situation and can see the scissors!!
I put the answer exactly as it came up in the 'correction', so you would have lost a heart either way. Disheartening...