Plenty of websites out there being kept up by volunteers without hardware access, the original owner having died or otherwise gone MIA. It's not always possible to add https, particularly when the site owner died 10 years ago and someone has an 'agreement' with the hosting provider to keep a website up as a memorial. No, I don't have any specific examples right now, but anecdotally I occasionally come across a website that's been in such a read-only form for as long as a decade due to family members being willing to continue paying the $15/year hosting fee, but not having the technical knowledge, passwords, or interest to fix problems. Sometimes there's evidence of a partial upgrade (the search engine stopped working due to a php upgrade), or a forum that has been converted to a static site entirely (the login buttons don't work either). In any of these cases, getting LE working is almost certainly more trouble than it's worth for whoever is currently paying the fees.

I have an old Linode with 4-5 personal sites running off a single Apache server. Until recently, it was running Ubuntu 10.04 LTS.

It took me a few days to safely upgrade to a new Ubuntu version with a new enough Python to successfully run letsencrypt, without also breaking the weird custom apache configuration rules that had accreted over the years.

I'd imagine lots of hosts don't allow users to setup Let's Encrypt so then the obstacle is first migrating to a host that does allow it (or includes direct support for it).

As a user, I don't care. If Google is preventing me from finding a site I want just because it's not using HTTPS, I count that as a fault with Google, not the site.