If someone have experienced supernatural abilities through meditation, than why don't he shows it to world? If somebody goes beyond fourth jhanas and has received super knowledge and also powers, than why don't he shows it to world and shares his knowledge and experience to world or say scientist and science community so that the general humans will believe in dharma and religion?
The objective of Dhamma is the work yourself out of stress and misery which is to follow the Noble 8 Fold Path. These kinds of practices diverts from this focus. If someone start practicing being attached by such display then most likely their goal will not be tied with the Buddhist goal.

Perhaps for this reason monks are not supposed to display such abilities. Even for lay, through there is not rule, it is not advisable as you are diverting the attention and focus from the true purpose of the practice. Also then meditation practitioners will be no different from magicians and illusionist, like David Copperfield. People will go to them to learn magic tricks and not to learn the dhamma with a view to Nirvana. People go to see David Copperfield for entertainment and not spiritual guidance! Also when displaying these abilities one might develop pride which would lead to one's downfall.

Displaying these abilities may attract a following and belief, but for the wrong reason.