The problem the tweet is pointing out is that research scientists are mostly concerned about getting and keeping funding since their jobs and the jobs of those working for them depend on it. Thus they'll target research questions that are deemed sexy by those in control of the funds. This can lead to a few areas being over-researched and other worthy areas of inquiry being underfunded. Plus that over-researched work can be of questionable quality and importance since a lot of less-good scientists get funded due to the overabundance of funds.