I think the rules about self-promotion are well-intended. If you ever get quora results to common programming or technology searches, you'll see what I mean; people responding with only loosely related comments which link to their own product, which "solves the problem for you". I get it, without any moderation, SO would be just as useless.

I think there should be some nuance in how those rules are applied. The author of this post appears to be one of the authorities on webgl. If they've written helpful posts on the topic, and those can be referenced from SO answers, they should be able to do that. Heck, even if they sell something on their blog, it's still highly relevant. It's same the problem Google, Youtube, Apple, and basically every other service right now is having with attempting to moderate what can be shared on their platforms, without losing the quality content. Incredibly often, they end up throwing the baby out with the bathwater.

I don't have a solution; the problem is in promoting quality content while preventing spam. It's not all-or-nothing, we need to strike the right balance with moderation.