[nospice]

That's a cynical take, so it will probably get upvoted, but what are you basing it on?

Ebay is a pretty eclectic marketplace and I can think of a number of possible reasons that have little to do with ads. For example, they may be worried about high error rates, and thus buyer and seller dissatisfaction. If I instruct an agent to buy X, eBay is almost never interchangeable with Amazon or Target.

They have no problem surfacing their listings on Google Shopping.

[pwg]

But, ads directly correspond to revenue stream, and a loss of ad "impressions" would result in a reduced revenue stream, so a "protect the advertising" response is not at all unusual to consider as a portion of their (eBay's) reasoning for this ban.

Given how hard they push sellers to purchase their "extra cost listing enhancements" (i.e., purchase to have your listings show in the "advertisement" spots) it appears that they may make a decent revenue stream from these advertising angles. An AI-agent could find listings without going through the advertising displays and as such cut into this revenue stream.