OpenBSD's ifconfig did not stagnate. It handles aliases, bridges, wifi, etc.
No, the issue is that no one at GNU or Linux cares about correct, simple tools (2 APIs for networking in the kernel?! What happened to manpages?! WTF info?). And thanks to that it runs on anything.
I'm not sure what the point you are making here is. The developers behind "ifconfig" on Linux could support the new API (iproute2) just as the developers behind "ifconfig" on OpenBSD updated their software to support the new kernel API as they became available.
Nothing stops anyone from offering patches to multiple projects to sync development. Hell, some of the biggest changes crossing the kernel/userspace divide have just that.
No, the issue is that no one at GNU or Linux cares about correct, simple tools (2 APIs for networking in the kernel?! What happened to manpages?! WTF info?). And thanks to that it runs on anything.
Pick your poison
https://man.openbsd.org/ifconfig.8