I can remember asking my daughter if she had supplied her daughter with two lots of bedding when she started university. She asked me 'Why?' - and I said for when she changed hr bedding. My daughter laughed and said she would probably do that when she came back home at the end of each term.
I know my daughter changes her own bedding regularly, but she told me that her teenage daughter rarely put her sheets etc. into the washing basket at home.
I change the bottom fitted sheet fortnightly, pillow cases weekly, use a flat sheet between me and duvet and this is changed fortnightly, but turned top to bottom and different side to me in the intervening week. I only use a duvet in the winter months, and change that cover about every four weeks. In the warmer months I just have a coverlet over the flat sheet and this is washing, monthly.
I do air my bed each day. Leaving it stripped back for about a good hour or more each morning, between getting out of bed, having my brekkie, etc. then going back into bedroom to get showered and dressed and make the bed.
Think we are all rather obsessed these days with cleanliness almost to a point of it being unhealthy.