If eBay thought having storefronts would be advantageous, they would have them. It doesn't make a lot of sense for eBay to merge with Gamestop only for the combined entity to decide that the most sensible first thing to do is close all the Gamestop locations.

The physical Gamestop locations are also horrifically overprovisioned to be an eBay storefront. Many companies have already experimented with things like "lockers" which seem to be successful enough to hang around, probably because the costs are low enough they don't need to do much to justify themselves and they don't need dedicated store fronts. If they want better assurance that the things being shipped are what the sellers claim they are a partnership with UPS or Fedex and their wide variety of existing storefronts that are already provisioned with everything you need to ship almost anything makes orders of magnitude more sense, and nobody has to "acquire" the other to make that work, without the square footage of a Gamestop location.

GameStop's idea behind using their physical locations isn't for ease of shipping so much as ease of verification. People buying brand-name stuff off eBay (and Vinted, etc) pay for verification services to make sure that it's real. The idea - which is the only good/sane part of this entire takeover proposal - is to have retail locations that do the verification in person instead of shipping items to a central location for verification on sale.

But if eBay thought that would bring in more sales, I doubt it would be hard to find empty retail outlets in every city/town in the US and Europe since high street retail has been on a death spiral for years.

You can already use lockers for delivery/drop off with eBay through their courier company partners, at least in the UK.