It's quite possible to make a film with it, the question is could such look better with something else.WHY couldnt you make a film with a cam like this? what am i missing?
A f2.8 lens and 4/3 sensor will define the minimum depth of field for any given angle of view. If that's OK for the filmmaker, fine.
If less DOF is desired, the only way to get it is with a faster lens and/or a larger sensor, and if we assume 4/3 in all cases, that means an f2 or ideally faster lens. Practically, you're only likely to find such in either a prime or at the very least a small range zoom. And to use such you need the ability to change lenses.
It's worth saying that going for a built in lens greatly simplifies the optical design, which means a cheaper product than is likely to be the case if the lenses are interchangeable.