That would be reasonable for most people. The problem is that for some GPs that's not enough (there's a thread on Mumsnet about GPs complaining that seeing their GS twice a week isn't enough and they want more!), or they aren't willing to compromise, and there are some GPs who are overbearing, critical, or even toxic. Why would a parent want their child around someone who behaves worse than their child? What kind of example does such a person set?
The other problem occurs when GPs decide that they want to go to court because they want to put their desires ahead of the best interests of their GC. That's a problem. That's a very serious problem. If you truly have the best interests of the children at heart, why are you putting the family through the stress and expense of court? Even without attorneys, there will be court costs, child care costs, and time off work involved. That's money that isn't available to support the child's basic needs, not to mention the stress on the family. If getting time with your GC is more important to you than them having enough to eat and a healthy environment, then frankly, you're someone who has no business being around children.