If the developers wish to provide a Steam version with their work on itch.io then they can add Steam keys on itch.io via the “External Keys” functionality. If they have done this, you can access the Steam key with your purchase via your purchase page.
For some of our larger charity bundles, we explicitly disable Steam keys with the purchases. If you’re referring to our Palestine or Racial Justice bundle, then no Steam keys are included. This was written directly on the bundle’s page and the purchase dialog. The point of those bundles was not to claim as many steam keys for as cheap as possible.
We ask that you do not pester developers about adding Steam keys to their page or giving you a Steam key. It’s their decision about how they wish to distribute their work. Comments left on developer pages about giving out Steam keys will be picked up by our spam detector and deleted.
Hope that makes sense,
Thanks