I'd like to digress to your "Encouraged more forcefully" phrasing which is quite interesting if you think about it. In my view, it would mean something like pervasive dialog box ala EULA, some UI hoops you need to resolve, alike going with local account on installation.

In reality they done basically everything to force users to use secure boot. If they disabled normal boot altogether, OS adoption would suffer heavily. They could've obscured that option, but it would be found out, and enterprise users would be pissed at them because they didn't gave them a provisionable way while the way exists. So it came down to normal variables in installer registry.

However modifying, e.g making users "hack" the ISO is really as forceful as it gets without market loss.

Note: There may be more normal way today than modifying the registry of ISO, I installed 11 once when it came out.