> There must be a lot of unmaintained PHP codebases that will break if PHP is updated by hosting provider etc.
Tons of them. If PHP really powers 50% of the internet, as they say, then maybe 25% of the internet is running an out-of-date PHP version. Then get into out of date Wordpress installs (can't risk breaking that plugin) and Magento 1 installs (out of support for half a decade, still in widespread use) and remember that they can't even update PHP without updating the Framework. In general, Laravel is sometimes better if the devs have been upgrading every LTS or so, that's once every two years. But if they miss an LTS, Laravel installs fall just as fall behind as any other framework.
> Someone must be pulling a lot of hairs because of this.
No, nobody really cares. Sometimes I'm paid a lot of money to fix things, though, so I'm not bothered by the situation either. It seems that once a site is passed to the content managers, the only way to budget for upgrading the site is when there is a problem. Never mind that they might have some small internal dev team adding features all this time.