CPU speeds stopped increasing because the market stopped focusing on CPU speed (coincidentally to this discussion, the change was largely to reduce power demands). Transistor count has kept plugging right along;
I think it's the other way? That is, market stopped focusing on CPU speed because they hit the wall and clock speed could no longer be used as a differentiating factor.
I think it is misleading to say it was due to reduce power demands. Rather it was due to needing to cool the damned things. If you were to have a 500W TDP chip, you would either need a crazy huge cooling system or a much bigger surface area. Consumers want light and thin, so Bob's your uncle.
Even if consumers were fine with big heavy things (and except for maybe phones, I don't think the CPU weight/size are an issue for consumers), light travels roughly 1ft/ns. You want fast, you have to be small.
Surprised by the negative reaction.. More technically, processor speeds required far more electricity to increase clockspeed which required much more energy to disappate in the form of fans and heatsinks.
