I'm not so sure how "easy" it is to repeat all real life experiences in PubMed studies, especially when it comes to items which contain multiple synergistic compounds or a protocol which has many features - both of which apply when it comes to much of the real life success of oleander and a great many other successful natural and alternative therapies. One thing I can assure you of is that it is extremely expensive. Where is the hundreds of millions in funding going to come from and, when it comes to oleander, what exactly would be the incentive when companies have already patented oleander extract and put it forward into FDA trials?
If all you accept is PubMed studies, then you are a bit out of place at this site. It was specifically created to provide information about items which are largely outside the limitations and mainstream control of mainstream medical science and practices.