Pretty much any legacy system can have a modern reverse proxy in front of it. If the legacy application can't handler certs sanely, use the reverse proxy for terminating TLS.
"Just use Nginx" was not a viable option here, without additional Certbot etc. orchestration, until 14 days ago! And this is still in preview! https://blog.nginx.org/blog/native-support-for-acme-protocol
And, if you haven't been using a reverse proxy before, or for business/risk reasons don't want to use your main site's infrastructure to proxy the inherited site, and had been handling certificates in your host's cPanel with something like https://www.wpzoom.com/blog/add-ssl-to-wordpress/ - it is indeed a dedicated project to install a reverse proxy!
Imagine you run an old-school media company who's come into possession of a beloved website with decades of user-generated and reporter-generated content. Content that puts the "this is someone's legacy" in "legacy content." You get some incremental ad revenue, and you're like "if all I have to do is have my outsourced IT team do this renewal thing once a year, it's free money I guess."
But now, you have to pay that team to do a human-in-the-loop task monthly for every site you operate, which now makes the cost no longer de minimis? Or, fully modernize your systems? But since that legacy site uses a different stack, they're saying it's an entirely separate project, which they'll happily quote you with far more zeroes than your ads are generating?
All of a sudden, something that was infrequent maintenance becomes a measurable job. Even a fully rational executive sees their incentives switch - and that doesn't count the ones who were waiting for an excuse to kill their predecessors' projects. We start seeing more and more sites go offline.
We should endeavor not to break the internet. That's not "don't break the internet, conditional on fully rational actors who magically don't have legacy systems." It's "don't break the internet."