It's an odd notion that newspapers deserve or somehow own advertising revenue. But besides that, the horse is not just out the barn, it's already been served up as dog food.
Adding: that advertisers are so clearly willing to change platforms shows some combination of 1) you offer nothing particularly unique or advantageous for the advertiser, and 2) your publication gives no reason for potential advertisers to feel loyal or to seek brand association
I think there's something even more profound going on here, however. I've long felt that the value of advertising *to advertisers* has always been oversold, especially the old display ads in the local newspaper...