If the iterated integral is not first converted to its inert form, Maple will immediately seek an exact evaluation of the integral. When it discovers that it cannot find the appropriate antiderivative(s), it then switches to numeric mode. Since it can take Maple quite some time before it gives up on the search for an exact value, if the user knows in advance that a numeric evaluation is called for, it should be initiated immediately by first converting the integral to inert form.