Tenants probably don't want to have to go so didn't tidy up for the EA. Landlord and EA can't force them to make it look like a show home.
I know someone who bought a house like this in London. Tenants were in when they looked round and told my friend repeatedly that they were annoyed the landlord was selling - tried to guilt my friend into not placing an offer. Once the sale went through and all the tenants clutter was gone it felt a lot bigger.
I do feel for tenants who are at the mercy of landlords suddenly deciding to sell. I can see why they don't out the effort in to cleaning/tidying before photos or viewings.