It’s not just them, it’s the media, politicians in the US and Ukraine.
Ukraine might have some success using the F-16s, in the end they have no experience flying the planes, especially in a combat situation, Russia has capable air defense systems, perhaps not the world’s greatest, but capable. It will be leading lambs to slaughter.
Russia’s S400 is rated #1 air defense system on the planet by numerous military publications and sites. There may be some disagreement here and there about first place, but they undoubtedly have one of the world’s best ADFs.