CMS Rot
Let us introduce the notion of "CMS Rot". It's not unlike the phenomenon of having to buy new "smart" "phones" every few years for a new version of iOS and Android, otherwise "apps" would no longer be compatible.
With "modern" (bloated) content management systems (CMSs) there is a long chain of dependencies, ranging from the CPU (32-bit for instance) to the kernel, the webserver, PHP, database and all sorts of "modern" Web "frameworks" (piles of bloatware with lots of bugs and vulnerabilities waiting to be found). If your site relies on "old" CMSs, or if your site does not use some very "modern" hardware and "modern" database, then no luck. No pages, no administration... nothing.
Upgrades can be complicated, especially on systems with many tenants and many bits of software residing side by side.
If you think of offloading or outsourcing all this to a company/site like TypePad (to manage it for you), then oops. Sorry. TypePad is shutting down this week (tomorrow). If you buy from Automattic their ridiculous package:
They can also sell land on Mars to the same people. The Web won't last this long and Automattic already has many issues, so it might not even last 10 more years.
As we put it 2 days ago: Web Sites That Are Independent Are Also Like Software Projects (Sometimes Literally So) █