Why is it that firms can earn profits in the long run in monopoly and oligopoly but not in monopolistic competition and perfect competition?

Because monopolistically competitive firms have an optimal production allocation at monopoly values: marginal revenue = marginal cost, marking-up to the demand function. When competition is not perfect, marginal revenue does not equal demand but is always below it on a Cartesian plane, so the optimal production value of a monopolistically competitive firm is both less and at a higher price than a perfectly competitive one.