I used to do consulting for companies that weren't connected to the Internet yet. This was the early-mid-1990s and "Private IP Network" assignments literally did not exist until 1996.
Therefore, people who weren't on the Internet yet, or didn't expect to be connected to any particular WAN, or even had their own intranet WAN without public access, they improvised like crazy. Like, whatever IP address ranges worked for them, they just plugged 'em in.
Since it was indeed early, and IPv4 networks were being handed out like candy, the savvy companies just applied for their own network space, hopefully of an appropriate size. The applications at the time didn't specify or require that they route the traffic or put it into BGP, so registering your intranet with IANA was the right thing to do, and future-proof. Unfortunately, in the wild-west early days before CIDR, IANA needed to find either a chunk of class C, or class B without significant nuance. And that is how Apple, HP, and Ford came to control gigantic swaths of "Class A" space.
Renumbering private networks was one of the nightmare scenarios of consulting firms like mine. And it hasn't really stopped, I suppose. If your company does an M/A their private LANs may clash, and they either renumber or they NAT.
By the way, OpenWRT isn't supposed to be using ".lan". That's a ridiculous non-compliant behavior. Someone should've stopped that, long ago.
There are ways to subdomain properly and IETF has provided dedicated TLDs for it even now, but back in the day, it was not easy, and I get it. When I needed DNS for my homelab, I discovered that the best practice among bad practices was to subdomain your ISP's. Like, make up a fictitious subdomain and hang it off their real one. Then your DNS had an anchor in reality, even if it was all made up, never delegated, unreachable, unresolvable from the outside.