Because laboratory glassware is very expensive and that would be massively wasteful? Also, most labs that I have been in make regular use of custom made glasswa

Because laboratory glassware is very expensive and that would be massively wasteful? Also, most labs that I have been in make regular use of custom made glassware. Most chemistry departments employ a glassblower! Also, for very sensitive experiments, you would most certainly want to clean even brand new unused glassware. Glass is amazing for chemistry not only because it is chemically inert, transparent, has a high melting temperature, and is reasonably strong but also because it is easy to clean!