Banners were a great idea, but I put bitly links on them to track the click through rate and I have to be honest, nobody clicked them : ( Maybe my banners were just bad, but I had a few thousand readers on my comic, so you would expect more interaction.
With them not being on mobile, a large part of your readership won't even get to see them as Jack correctly states. I understand why the Tapas team considered removing them.
But I also understand that people are sad to see them go.
They were pretty neat, just not as essential to success as one may think.