-There is hydrogen in Enceladus's plumes which implies there are hydrothermal vent(s) on its sea floor. This has gotten scientists excited because of the ecosystems around hydrothermal vents on Earth.
-Hubble has observed multiple plumes in the same location on Europa, which would be an ideal location to sample water without a crazy drilling operation. There are also 'hotspots' on the surface of Europa which coincide with plume locations.
-NASA people still suck at speaking to the public (and I need to take more time writing a post like this so I don't have to edit it multiple times).