Just like most people are reluctant to make use of new technology in their houses in favor of the older ones, you find a lot of people sticking to glass barware rather than going for plastic barware. They figure that if they went for the plastic variant of the barware, it would look like a cheap alternative. As conscious citizens, they would not want people to get the wrong idea about the economic situation. This is the primary reason why people are most reluctant to make use of plastic barware.
However, there is also a growing popularity in the use of plastic barware, and it has to do with the young generation. Organizing parties takes up a lot of time and money, and hence there is precious little money which will be left for purchasing barware. This is the primary reason as to why most of the party is now feature plastic barware. Moreover, there is a lot of safety associated with plastic barware, and one can generally witness cups lying in the ground. If this was made out of glass, then there would be shards of glass everywhere, causing potential damage to the guests in the party. With the presence of plastic barware, such accidents are not possible.