It could also indicate that it’s relatively cheap to sit on domains for 20 years, patiently waiting for someone to pony up. It’s not like valuable domains are more expensive to renew.
then maybe it should be forbidden to renew domain if you haven't use it for a year instead of increasing prices for everyone, how convenient for domain registrars
How would they define “using it”? I’m guessing there would be easy ways to skirt around any automated system that checks for whether a domain has been used. Update the text on the “for sale” landing page? Look, I used it!