Because ye ask amiss (dioti kakōs aiteisthe). Here the indirect middle does make sense, “ye ask for yourselves” and that is “evilly” or amiss (kakōs), as James explains.
That ye may spend it in your pleasures (hina en tais hēdonais humōn dapanēsēte). Purpose clause with hina and the first aorist subjunctive of dapanaō, old verb from dapanē, cost (Luk 14:28 only in N.T.), to squander (Luk 15:14). God does not hear prayers like this.