I can think of a number of reasons:
1 no one can do what is claimed;
2 people can do it but not consistently or on demand:
3 mediums are frightened of public ridicule by organisations they don’t trust;
4 they don’t need the money:
5 even if they are genuine, mediums think they will be misrepresented;
6 the conditions they are expected to perform under are not what they require;
7 the do not need the endorsement of sceptical organisations;
8 they are happy to do their work to a standard that satisfies their clients.
There are probably loads more.
There are a few examples where mediums/psychics have been examined by sceptical organisations and misrepresented. Why put oneself in a position where the chance of winning seems small but the consequences of failing for any number of reasons could be public humiliation?
1 no one can do what is claimed;
2 people can do it but not consistently or on demand:
3 mediums are frightened of public ridicule by organisations they don’t trust;
4 they don’t need the money:
5 even if they are genuine, mediums think they will be misrepresented;
6 the conditions they are expected to perform under are not what they require;
7 the do not need the endorsement of sceptical organisations;
8 they are happy to do their work to a standard that satisfies their clients.
There are probably loads more.
There are a few examples where mediums/psychics have been examined by sceptical organisations and misrepresented. Why put oneself in a position where the chance of winning seems small but the consequences of failing for any number of reasons could be public humiliation?