Why can't we just have toilets?! A toilet and sink in a small enclosed room for anyone to use?
Simply put, space. you can fit 2-3 normal cubicles in the space of one accessible one, and 3-4 urinals in the same area of space.
This would also help with queuing. The nonsense of queuing for a ladies toilets when the mens is empty is insanity.
It wouldn't though - it would mean fewer toilets, which means just as much queuing.
There are ratios of how many urinals, to how many cubicles, to how many people that you need for it to be fair - this has all been examined and analysed, we know all this.
The only issue is some people deciding that they want to use the toilets for the other sex, and women having a problem with that. It seems every solution others come up with just puts women at a different disadvantage, all to avoid just telling these people to do what's always been done and use the mens if you're male.