Substitute ads and or content is *usually* because of licensing, or lack
of...

Wrong. Substitute ads on the stream are because of AFTRA fees. Fees
charged for material run on the Internet are 300% of what they are on OTA
radio.

PSA's also make a station look good at license renewal time...

Wrong again. PSA's run on the stream have no relevance to the license
renewal process. Nor, for that matter, do PSA's run OTA.