If shilling sites are more likely to be SEO-optimized, yes. One of the implications of Bayes' Theorem is that if observing A makes B more likely, then observing B also makes A more likely. A worked example:

Given:

P(shill) = P(!shill) = 0.5

P(optimized|shill) = 0.8

P(optimized|!shill) = 0.6

Then:

P(optimized) = P(shill) * P(optimized|shill) + P(!shill) * P(optimized|!shill) = 0.4 + 0.3 = 0.7

P(shill|optimized) = P(optimized|shill) * P(shill)/P(optimized) = 0.8 * 0.5/0.7 ≈ 0.57

P(shill|!optimized) = P(!optimized|shill) * P(shill)/P(!optimized) = 0.2 * 0.5/0.3 ≈ 0.33

Yes, because knowledge isn't SEO-optimized by default. It takes time to do so. And time is money. And 99% of the time, those who are willing to spend a lot of time to get on the first page of Google are doing it to gain money, not to spread knowledge.

I don't disagree with your main point, but spreading knowledge and making money aren't mutually exclusive.

> Yes, because knowledge isn't SEO-optimized by default.

Isn't it? I thought Google was trying to optimize their search engine for finding useful information, so if someone were to make an honest website that just tries to provide useful information (anachronistic as that may seem) wouldn't they hypothetically have the full manpower of Google's search team optimizing for finding it?