For poor durability, stopped producing legends blank?
Blank keys do not have legends.
There are several ways to install legends on key caps. The most durable is "double shot" where the legend is extruded first in one color and the body of the key is molded behind it in another color.
Dye-sublimation means that dye is absorbed (sublimated) into the body of the plastic so that it is not just a film on the surface. These are also extremely durable.
Pad printing means that the ink or paint for the legend is applied to the surface only and will wear off sooner or later, depending on the quality and thickness of the paint as well as the body chemistry and cleanliness of the user.
Laser can be a light application that merely causes the surface to become discolored, or etching which is a process where the stronger laser is used to melt a canyon into the surface of the key cap, which may or may not then be infilled with contrasting color ink.