Products made of glass are more expensive and more difficult to make by the manufacturers, so they have to charge more than the plastic products. Many vapors choose what they use based on price, so they will buy the plastic ones over the glass ones. Many vaping novices are unaware that some flavors can destroy plastic juice attachments.
Polycarbonate plastic is the material that is succeptible to cracking/melting. It is cheap and easy to form into shapes for manufacturers to use. Polypropylene (frosted or opaque) has a different chemical bond and is immune to the flavors that crack/melt polycarbonate, however it is difficult to mold into the shapes that common clearomizers use.
More customers are demanding products made of glass, and a few manufacturers have listened. The last year has seen a doubling of the products made of glass.
Something Safe for Cinnamon & Citrus Flavors
The above blog link describes why certain flavors destroy polycarbonate, shows a video of a tank melting after exposure, has a list of flavors known to cause this phenonemon, and many recommendations of attachments which are safe to use with the caustic flavors.