There is probably no simple answer to this very relevant question.
Looking at the expected advantages with LENR Energy, most people hearing the first time about it reacts with a large and understandable skepticism, “all these fantastic advantages and no one talks about it, it can’t be true“. Established scientists often react a bit different, “our physics standard model does not allow something like LENR ” and “if it was possible it would have been discovered already“? Still, there are already several LENR related articles showing some abnormal heat generation but none has yet been accepted and published in a reputable peer-reviewed scientific paper. As long as there are no repeatable experiments with significant energy gain and INCLUDING a scientific explanation fitting the mainstream physics model, most nuclear scientists still totally reject all results from LENR related research.
Many try to put the present LENR ignorance from the scientific community on the official announcement by Fleishman and Pons about the discovery of Cold Fusion (now termed LENR) in March 1989. In front of worldwide media and the whole science community, they claimed to have detected abnormal heat from nuclear reactions in an electrolysis cell. Unfortunately, their experiment turned out to be extremely difficult to verify and their proud announcement was soon regarded as major fake news by both the media and scientific community.
From 1989 up to now everything connected with LENR was treated by mainstream science and media as scientific humbug and majority of investments in renewable energy the last 30 years has instead been directed into solar, wind, new generation fission generators and to a very large part the international projects to replicate the fusion process of the sun, such as the ITER and similar projects. Results of developments in solar and wind must be regarded as quite successful while the attempts to tame the hot fusion, although enormous public investments are still lacking real significant visible success.
The community working with LENR research seems to have learned the lesson from 1989 and most are not officially presenting their results until there can be no dispute of success. Now it seems that after 30 years of works in the dark, 2019 started with a possible game-changer, the first public presentation of industrial LENR Energy in real production.
Also recently (March 2019) a well-balanced article summarizing the progress of LENR Energy to date was published.
At the moment we choose to leave for the science history writers to find the real answers to why LENR was never put in focus for mainstream research and investments. But if you cannot wait there are already several books written on the sometimes quite dramatic history of Cold Fusion or LENR as is the term used nowadays.