While those are great niches that have a high CPC ratio, they are by no means the ONLY niches out there in which you can make money. In fact, I'd argue that they're harder than other highly searched niches that don't require as much work to rank on the first page of Google for.
You can still get good income in adsense even if you are targeting low-paying keywords. It's all depends on your research and hardwork in promoting your site.
You can have a good income with high paying keywords as well. You just have to know how to get traffic for them. It's not hard if you know a few tricks of the trade.
Actually the point is these subjects can get high clicks but it all comes down to traffic. What about a site that gets 100,000 hits a day with clicks of 10c each compared to a site that gets 100 hits a day with $10 a click. It's all very well looking for high click keywords but you can still make a lot of money through low paying click words too.
You are not wrong but the problem is that there are too many people trying to create blogs and websites related to these high paid niches therefore you will get very little traffic even you spend much effort. Only if you do have very good content and strong advertisement that you will get success. You will have to spend much money too.