“...maybe remembering to update listings is the last thing they worry about and tends to be neglected?
”
Without a doubt this is a big part of it. But if you are pinged and reminded to update your details, and then decide to ignore, or haven't updated contact details so you never get reminded, then maybe directories (me included), social media platforms etc should be more ruthless and simply delete the data.
Would at least clean up the search engine index with a lot of unwanted rubbish. But will confess to needing to get my own house in order

(dumping 220,000 old listings tonight

)