Because of several reasons, you might call excuses.
The only evidence available is through the agency of physical mediums
All our accepted knowledge does not include the paranormal.
Religious Churches and orthodox science are generally very anti for their own reasons. It is not a religion as such.
Physical mediums have more or less died out, for various reasons
The phenomena is unpredictable and not controlled by the medium and circle
Some of it can be spontaneous and therefore not occurring under test or circle conditions
The "energies" or attitudes of sitters can affect the results.
I am unable to produce evidence because now I have no access to a physical medium to give evidence
When I did sit in seances with a physical medium for a year, I did experience some evidence to back up Crookes.
That evidence like the table tilt I described is not believed by anyone here, which is quite typical
I now know another physical medium, whose circle is said to produce phenomena, and communication by voice. I have visited and investigated, and examined the physical evidence from the seances they had. This included apports, and writing on pieces of paper brought in from outside the room by an unknown agency. This is their evidence, not mine, and it may or may not be genuine phenomena.
Next step, I intend to sit with that circle when they invite me, and see for myself. I will draw my own conclusions from the evidence. Again we are no farther forward really, I would not expect you to believe anything outside normal laws.
If for example you were then invited, you accepted, and you experienced phenomena outside the laws of physics, what would you do? Nobody else would believe you as it is too wierd to take for most people.
Even if a team of scientists came in with all sorts of equipment, what would that prove? Would they be trusted, would they affect the conditions, etc etc. They write a report about what happens, and we're back to not believing books and accounts again.
This is wearing my brain out! Hope it 's worth it. If you take any note of the Society for Psychical Research, they published "The Scole report" in November 1999. I bought a copy, in which they investigate the genuineness of a range of physical phenomena with a mediumistic group. There you will see full descriptions of all they did together. 447 pages. There are photos of the evidence they received as well as the accounts. It takes some effort to wade through it, but it enables you to make up your own mind on the contents. However, it is only a book. like all the others. is this evidence you would accept?