[soneil]

I think what really stands out about this, is that having it installed as a pre-made brick is very cost-effective.

But this cost-effective route isn't readily available to most people, as most people don't build homes. Developers build lots, and then sell finished homes. So you need to entice developers. And historically, "the stick" is the only enticement developers remotely pay attention to.

"If you want a swift brick, install one yourself" is much easier said than done - you're talking about removing an existing brick, replacing it, hoping you don't damage the course or the cavity, probably voiding any warranty on a new home, etc. It's certainly not a £35 retrofit.