This was mentioned in 2019 Early Seller Update. Here is https://community.ebay.com/t5/2019-Early-Seller-Update/Update-on-Good-Til-Cancelled/td-p/29556571:
"Hey eBay sellers, this is Harry, VP of Seller Experience at eBay. As you read in the 2019 Early Seller Update, we are moving all Fixed Price listings to Good ‘Til Cancelled (GTC). As a reminder, this change does not apply to auctions. We’re making this change because we have seen that GTC listings offer more sales opportunities than any other fixed price duration. Over time, GTC listings keep and grow watchers, sales history, and SEO authority as they maintain the same item ID and URL for the life of the listing. We believe all of the above improves the ability for buyers to discover items on eBay, which thereby improves the likelihood of a sale."