Why YouTube Link in <Video> tag?
eBay announce in 2016 about active contents which includes <object> tag. In mid 2017, eBay implementing new policy for all listing.
Please visit http://sellercentre.ebay.co.uk/business/active-content for more information.
eBay already don't allow <iframe> tag for YouTube video and in 2016 eBay announce they going to remove <object> tag also because it also active content. Only they going allow <video> tag which no support YouTube link.