I originally found the 20 most expensive ad words post on wordstream, a company that specializes in helping companies finding the right way of advertising online, including selling google ads, aka adwords.
When it comes to head to head competition, the company that is the top of the list usually makes most money. This is specially true for internet, considering the way people analyze webpages #1 link being most clicked and watched overall. So you want to be on top, so you have to pay for it.
The next component is the revenue per click, aka margins (price – costs). The higher the margins in an industry the more companies can give to find a new customer. This creates the bidding war where the most expensive words will correspond to the products where the words with the highest margin. The most value afterwords follows not from selling the product ones (so called “one-offs”) but rather have a continuous flow of revenue over time (“subscription” type service). This is what we also see in the graphic bellow. It is not the “cars” or “jewelry”, but rather “insurance” and “mortgage”. Some of the founding even surprised me.