Your numbers don't check out, please provide sources. The Linux Kernel has around 40 million lines, the OpenBSD kernel around 7. You might have mistakenly counted OpenBSD/NetBSD as a whole system (the base installation), instead of solely the kernel.

Given BSD is supposed to be a complete package while Linux has a separate kernel and userland, that's probably why.

You're probabry including ports/ which contains all the software available for the platform

Is that more than the kernel? How much more?

One reason is that the coreutils in Linux use a lot of hacky or hard to read tricks to improve performance. OpenBSD explicitly wanted to make their source code more legible. FWIW I prefer the Linux approach.

This is why I typically refer to it as GNU+Linux and not just Linux. Two different and incompatible operating systems can use the same kernel just look at Android and GNU+Linux. Each of the BSDs is a complete operating system (userland + kernel).