"Is the Ebay market hurting new film sales?"
It's tempting to dismiss the question but the issue of film sales is interesting as well as important.
The answer to the question is 'no', regardless of the size of the eBay market.
eBay is a gray market mixed with an above-ground market. Call it a hybrid retail markt. Accordingly, demand for new and expired film on eBay reflects overall demand for film. Prices for both kinds of film on eBay are governed by the total market.
In no way should any individual feel compelled against or guilty for buying there, as it takes the respective units out of the broader inventory at a given price. It is what it is: supply. All use of film is good (apart from environmental impacts).
If the question is, 'How can we help keep the films we love in production?' that is an interesting question that maybe addresses our concerns more precisely. If there is not enough demand for film or for a particular film (that is produced with particular machines in a particular place), a manufacturer would be stupid to produce it out of charity.
We are seeing the discontinuation of important films by the big manufacturers, but the smaller factories are benefiting from this contraction of capacity.
I too would love to see worldwide sales trends. Ilford has this information but don't share it. The fact that they -- with their strong commitment to black & white -- and their new investments in direct positive papers (and a Walker pinhole camera to go with it) as well as their new Art 300 paper, these should be strongly positive implications that the overall numbers are positive.
Just because Kodak and Fuji are closing capacity -- and likely to close more -- this is not an indication that film overall is going away. Some of these capacity reductions will be painful. But scale in certain places is no longer supported by reality.