I actually been watching something about this and often houses that get little to no viewings are usually untidy/dirty, hoarded, unfinished or have too many indoor pets but on for 'full' price. People can see from photos they aren't worth viewing.
If something is dirty people assume not looked after so other problems.
If somethings hoarded people can't see the rooms or if there is problems.
If someone has dozens of unfinished jobs/DIY projects its sets alarm bells off about what they may have done without permission or bodged.
If someone has destructive indoor pets people know that will have big issues (smell/damage etc...).
These things should be really bloody obvious to a seller but some get so use to living as they do that they don't see an issue with it. There is not any nice way to tell someone their house is a filthy, stinky, bodge jobbed, overcrowded hovel though so people just don't waste time viewing them instead.
If the seller was getting lots of viewings but no offers then it might be price or something more hidden but why is no one booking viewing? most likely because something must be obvious from the photos. It could even be that they see the neighboring house is dirty/hoarded/abandoned/party house etc... or something and thus will be an issue.
A house we viewed had no photos online and was the worst smell I ever smelt (backed up sewers), big drooly dog making a mess, hoarded, damaged with awful structural issues and damp... it still sold though because it was 'cheap' (although not cheap enough for the work imo). So price does play in a bit even a nightmare house can sell but it needs to be low enough to tempt viewing if there 'obvious' issues.