Labor costs and cost of living. Americans get paid 10-20x more than the same job in China. It cost SO MUCH LESS to live in China. A frugal person can eat 3 meals a day for about $2. It’s not the best, but it’s affordable and nutritious.
US glass is better only because that person that says that is a nationalist. Better is a crazy word.
Better in the sense that more profits and labor stays in the USA.
But you must not look at all American glass the same. A garage blower that does not pay taxes, sells the glass under the table, is not a good citizen and that person is actually hurting the American workers that do pay the taxes and have proper safety.
Foreign glass is good for people that do not have much money. It is also good for someone that wants to try a piece of glass but does not want to get something too expensive now, not until they fall in love with what we have. Then they will want the American made for the artistry and good feeling of buying from your American sister or brother.