Why does early-userspace Linux not get enough entropy?

I have a hard time following the lines of thought in a recent LKML thread on what to do about prolonged (unbounded?) blocking of a getrandom call at system initialization.

The crux of the problem is the kernel neither getting nor creating enough entropy for an early getrandom call to succeed in a timely manner.

Linus Torvalds was, incomprehensibly to me, arguing for breaking userspace in that thread, changing the behavior of getrandom to error out with EINVAL. (Who stops Linus from breaking userspace?)

Arguably, it's the kernel that is at fault for not getting enough entropy to userspace even in early userspace.

(void *)getauxval(AT_RANDOM) in an init process already yields a pointer to 128 bits of randomness. (A C library may even make use of it to initialize things like the __stack_chk_guard value.)

Why can't the kernel take (those?) 128 bits to initialize a CSPRNG to be used by the kernel implementations of getrandom(..., 0) and /dev/urandom, enabling those interfaces to spew out whatever amount of pseudo-random values requested?

Apparently OpenBSD does not have this problem. Its arc4random_buf function always returns the randomness requested with no room for error. So I'm guessing the OpenBSD kernel can always get enough entropy to then initialize a CSPRNG either in-kernel or on the userspace side.

What were the choices that led OpenBSD to having an error-free function? And could the Linux kernel/userspace adopt those or similar choices for getrandom?