One of the principles of science is to question. If experiment after experiment produces no evidence and the hypothesis still calls for a rewriting of everything we know, it's safe to say that it is not true, i.e; homeopathy or the Earth resting on the back of turtles.
Personal anecdotes are not evidence, no matter how much one might want to believe otherwise.
And this ^^^^
But sheldrake has repeatable evidence. Why isn't it taken seriously? He obviously is very open about his research and encourages people to reproduce it.