If I were to pull on my statistical education and experience, I would postulate that there were more Jaigers produced than other kaijus in the Standard series. There are always some on Yahoo Japan, for at times half the cost of other similar vintage sofubi kaiju. Or it may just be that all the others are more popular. I have it on good authority that companies like Nitto and Bullmark did not keep records about production, so this will be nothing more than a theory.
Nitto's Ultra Kaiju Series had three sizes: Standard, Medium and Mini (also available as a Pendant...the same mini sofubi with an eyelet and a chain so that it could be worn). Unfortunately, Nitto did not make a middle size Jaiger, but the did make a mini (as seen above). I suspect the same sculptor that did the Standard Jaiger had his (or her) hand in this one as well.