"How about those guys that make motorcycle kits? No? Because too few people buy them to make motorcycle kits a thing?"
Might I direct your attention to http://www.tamiya.com/english/products/list/12bike/kit14001.htm , a page with the title "1/12 Motorcycle Series". Plastic model kits of, um, motorbikes.
For a UK vendor of motorbike kits, try http://www.emodels.co.uk/plastic-kits/-c-173_192.html which includes 4 pages of kits including Tamiya and Hasegawa products.
http://www.modelhobbies.co.uk/shop/plastic-model-kits-motorbike-model-kits-c-27_44.html has at least one non-Japanese brand...
So no, I suggest you try again with a different subject area.