According to the GIRM:
Sacred vessels are to be made from precious metal. If they are made from metal that rusts or from a metal less precious than gold, then ordinarily they should be gilded on the inside.
In the dioceses of the United States of America, sacred vessels may also be made from other solid materials that, according to the common estimation in each region, are precious, for example, ebony or other hard woods, provided that such materials are suited to sacred use and do not easily break or deteriorate. This applies to all vessels which hold the hosts, such as the paten, the ciborium, the pyx, the monstrance, and other things of this kind.
I don't think glass is considered "precious" anywhere in the USA and it would seem to violate the rule that the materials should not "easily break."
The issue that some parishes find themselves in is that someone had donated them in memory of a loved one and it can be a bit tricky for the pastor to change them. Sometimes the pastor is new and hasn't had time to make a change. Other parishes simply run on extremely tight budgets and its difficult to find a few extra hundred dollars to buy new ciboria .
However, be that as it may, you are correct that the glass is not permitted by the GIRM for sacred vessels.