Of course SETI doesn't explain "that there should be aliens here"! That's the point... it (or rather the persons involved) actively deny the possibility - even when the evidence is all around us.
That SETI also has a snow-ball's chance in hell of success, is merely another point as to why it should be scrapped as a reckless waste of resources.
I do wonder how you can at the same time claim that our atmosphere and near space is crowded with aliens, and that SETI does not have a chance of finding any of their signals.
