OP mentions that friend say main reason for 50/50 split is that they are sharing one bed with their spouses. I do not see anyone mention anything on the bathroom, that is 3 people in one room, using the bath. Sure, the couple has no problem being in the bathroom together, but I bet there is a bit of discomfort between the spouse and the other male traveling companion.

As others mentioned, having your own room will cost double, but if paying half is already a problem, it will ruin the rest of trip. You can only keep this up for so long before it bothers you.