Out of curiosity I looked this up. SMP was introduced in NetBSD 5.0 which was released 12 years ago. I think you're a bit out of date. :)
I'm wondering if it's a sarcastic comment in the style of the 'BSD is dead' meme.
You seem to confuse SMP with Intel's "HyperThreading", which is disabled on OpenBSD due to security concerns (SPECTRE et al.) and which makes sense to default to in an OS that takes security seriously.
SMP and HyperThreading are completely different things.