This is why some places like Michigan State University and Ohio State University use "desire path planning". That's where they observe where people walk and then install (or move) the sidewalks to match those footpaths.
It depends. Some people view lawns that aren't devoid of all insect life messy or trimmed evenly messy. And if it is raining or has recently rained, hardly anyone would use a muddy path so the concrete sidewalk will remain reasonably clean as well.
wheelchair-accessible
That's important, though I'm not advocating for keeping an entire campus unpaved. I am arguing that only necessary pathways should be paved while desire paths should ideally remain unpaved. People in wheelchairs should still get around (quickly), but desire paths don't need to be wheelchair accessible in my opinion.
I don't think there's an issue with desire paths becoming unusable during certain times though. It slightly extends the time you spend walking around but I'd prefer this over having unnecessary pavement.
You might as well pave the entire green space in this example.
I meant to convey how so much of the existing green space was paved already that paving the entire green space wouldn't be much different at this point.
I would guess the paved paths make up like 20% of the image? That's far too much in my opinion, green space in cities is already severely limited.
You can also see how every time a desire path was paved, new desire paths sprung up - which were then also paved.