It is quantity and popularity as well as quality. Most of us forget that the 1980's, the so called Golden Age of Mecha, while stuffed to the brim with new shows the reason for this was that companies were always trying to continue last season's success. For a decade thought to be so successful, it also say the death of two of the companies that contributed the bulk of mecha merchandise for Macross. Takatoku died quickly after Dorvack and Imai lost a lot of steam after Mospeada, Galvion, etc didn't live up to the success of Macross. After that, mecha shows started to thin out and the big companies settled into their current ways. Bandai bought Sunrise and now mostly focuses on Gundam shows with maybe one or two different things to fill the gaps. Takara tried revitalizing Votoms but stopped after Pailsen Files (there is literally no new Votoms merchandise as of this time) and now focuses on making more Transformers.
Also the rise of Video Games have created a new medium for mecha. Think of Kotobukiya, which is cranking out near Bandai level plamo kits based entirely on Video Game mecha. Not to mention the fact that many kids would rather play with the mecha in a video game than play pretend with a toy.
You guys are lamenting the slow death of real robot, but what was so special about it anyway? It's just a trend whose time has passed.