LXNDR: The difference, I assume, is that нагнуть (to bend), нанять (to hire, to rent) both exist independently as well-established verbs, to which the reflexive ending -ся can then be attached.

Similarly for verbs like находиться/найтись ("to be located," NOT "to walk till one is exhausted") -- derived by adding -ся to the existing находить/найти, "to find," and NOT by adding на-/-ся to ходить/идти.

In contrast, there's no verb наглядеть (at least not one in common usage); rather, наглядеться is formed by simultaneously adding на-/-ся to the basic verb глядеть.