Sometimes adding a user interface to a straightforward operation is complicated, expensive, time-consuming, and/or low-priority for the intended audience.

OpenBSD users know how to partition and encrypt their disks.

World domination was never on BSD's todo list!

Don't get me wrong -- the Linux way is also perfectly valid, and obviously more popular. But it's not the only way.

I think/assume OpenBSD is mainly used as a server OS. Yes, passionate people use it as a desktop but those mostly read the FAQ anyway.

Currently and as far as I know, bioctl does only support user typed in passwords or key disks. You certainly want also encrypted disks on your server but requiring user typed in password is oftentimes a no-go (think of various firewall appliances doing a reboot and not having remote hands). A compensation can be the key disk but I don’t know how widely that is used.

Hardware bound encryption like with a TPM is not supported. Also Linux is still exploring here as far as I can tell (no installer offers that).

In sum: I think disk encryption in the current form is not a tradeoff many installations will take.

Maybe it is coming now instead of earlier not because of a clear choice, but because to get features in to the project people need to spend their own free time on creating them.

Thank you Klemens Nanni and others for taking the time.

It's only now added as an interactive step in the install script. It has ~always been possible to create a crypto device with the install medium by dropping to a shell: https://www.openbsd.org/faq/faq14.html#softraidFDE

archlinux only added an installer very recently.

Besides, setting encryption manually and then installing openbsd with its very fast installer has always been faster than using the interactive debian installer so in the grand scheme of things it wasn't that big of a deal.