I posted this issue on woocommerce forum and its support staff said that my problem was related to the Google for WooCommerce plugin and asked me to post it to the Google for WooCommerce plugin forum. https://wordpress.org/support/topic/product-missing-merchant-listings/

I used Google’s structured data test tools https://search.google.com/test/rich-results found that most of my products don’t have Merchant listings, I compared their structured data and only kept the different code, see the following two codes
How to fix it?

According to Google search console, there are only 340 products with Merchant listings, and my store has more than 1000 products

Without Merchant listings
“offers”:[{“@type”:”AggregateOffer”,”lowPrice”:”36.00″,”highPrice”:”49.99″,”offerCount”:2,”priceValidUntil”:”2026-12-31″,”availability”:”http:\/\/schema.org\/InStock”,”url”:”https:\/\/www.sample.com\/store\/knitted-top\/”,”seller”:{“@type”:”Organization”,”name”:”Sample.com”,”url”:”https:\/\/www.sample.com\/store”},”priceCurrency”:”USD”,”hasMerchantReturnPolicy”:

With Merchant listings
“offers”:[{“@type”:”Offer”,”priceSpecification”:[{“@type”:”UnitPriceSpecification”,”price”:”79.99″,”priceCurrency”:”USD”,”valueAddedTaxIncluded”:false,”validThrough”:”2026-12-31″}],”priceValidUntil”:”2026-12-31″,”availability”:”http:\/\/schema.org\/InStock”,”url”:”https:\/\/www.sample.com\/store\/jacket-skinny-fit\/”,”seller”:{“@type”:”Organization”,”name”:”Sample.com”,”url”:”https:\/\/www.sample.com\/store”},”hasMerchantReturnPolicy”:

My System report: https://gist.github.com/Kenny19926/2fbc53dd19db0e87d4d2c27e13807b52

I use Google for WooCommerce to connect to Google Merchant

Google for WooCommerce: https://wordpress.org/plugins/google-listings-and-ads/

I also installed this plugin https://wordpress.org/plugins/woo-product-feed-pro/ ,and submit product feed to Google Merchant

Thank you!