One of the thing that comes to mind is that the license would most likely have to be accepted by the end-user (the person that installs the Singer component) in order to give due credits and also share the rights and obligations they have toward this component.

@micael_bergeron End user being whomever is running Meltano with the plugins? How did that work when Meltano was hosted?

The instance was provisioned with our own Taps (MIT licensed) for demo purposes. Users would then select which data sources they wanted and the corresponding components was downloaded and installed. Like I said in the OP, there might be a case for having a license agreement page at that step, but there wasn't in during my tenure there. Something along the lines of "This component is provided by …, the authors are … and you can find a copy of the source here. Do you accept to install it."

@micael_bergeron Oh wow, so even in the hosted version, it would have to download the tap/target as the user added it? Did Meltano create an instance of itself per user?

Yes.