You would have to distribute all these datasets with a license and such a thing would restrict any users much more than you'd realize - sharing one's results would become a trickier matter just for one. Deciding if the data is good would be another thing since being able to sell stuff produces an incentive for uploading garbage.

Just as much, huge datasets are effectively going to be the product of many people's data. If some entity decides it's going to profit from that, how do the profits get divided, especially if there's no protocols for that division.

For example, should someone be able to sell my chest X-rays if I haven't agreed to it? A lot of large companies with big data sets would face far more issues if they were to be selling those. And considerations go on and on and on.

The free-wheel, free-sharing quality of present day machine has been a driving force in its progress and it would be a shame for that to go away. As can be seen with the Internet, freely available data can be incredible force and hopefully data will remain freely available.