Does this become less true the more niche the website is? People who read my math blog should be served ads for technical things (math books, online courses, etc), regardless of recent search history.

In reality, I have a math blog with ads for Cap'n Crunch cereal and strange new yogurts which seem very distracting and poorly-targeted when compared to, say, ads for O'Reilly math/CS books or a MOOC on probability and statistics.