Sea Octoroks have never have never been quite as cool as Land Octoroks. Gamers have just spent a lot more time with Land Octoroks.
Nintendo haven't really made that big of deal of the Sea Octorok. I mean, in the original LoZ and ALttP and LA and stuff, you were always fighting Land Octoroks. But ever since Sea Octoroks were introduced in OoT you've just seen less of the guys.