I honestly am surprised by that as well (though: see mysterious Amazon Fantome outline ghost), but I think a combination of factors lead to this being less lucrative than it might seem. Glassware has only really had significant value for a couple years, and there's very little glassware that's really valuable enough to make faking it worthwhile. Most of that glassware also is traded within a pretty small group -- while there have been a couple instances of large finds (last summer's OG Yeti find, etc), someone random popping in with a dozen orange Cantillons would arouse some suspicion, and once you'd sold to two or three interested parties you'd find a very small market remaining. Also, a fair bit of glass at that level gets traded more than it gets bought & sold, and presumably if you were going to counterfeit you'd be more interested in cash. Plus, even when the model of glass is still made, it changes over time, so it would be pretty tough to get blank matches for some of this stuff (e.g. the Durobor Charente has gone through at least four distinct variations in the fifteen year range that I have).
I'm more interested in making glasses that don't exist but should