It doesn't make your getting a job harder. And even if it did, it's not your employer's responsibility to help you get another job. Do you think they should also be required to give you paid leave to go interview elsewhere? They shouldn't unreasonably hinder you, but they are under no obligation to help you go work elsewhere.

Also, no sane employer would be like "well this guy worked at a corporation that doesn't give references, guess I can't hire him." If you think that's how people who hire think, you must not hire. It isn't.

It would be a problem if a corporation gave references to some people and then declined to other times, because then it could be construed as negative, which is exactly why they have that policy.