Probably because the phone manufacturers seem to be so slow to produce new phones, only a few months ago at xmas i bought all my closest family android phones, sony xperia miro, sony xperia tipo, sony xperia u, and an htc desire c, everyone of them are ICS
Sony have only just brought a reasonably priced jelly bean phone, the sony xperia E
Unless you are willing to spend a fortune there is very little choice if you want a jelly bean phone
Tablets seem to be a bit better for some reason, there are loads of jelly bean tablets on ebuyer for under £100