Why is that? Undersea cables makes way more sense - the issue is we have maritime law that allows any nation state to freely roam over important cables. During wartimes this is a complete different story - ships won't be allowed near the lines, and if they do get close they will be destoryed without prior warning. No more anchoring "accidents".
It isn't either/or. Satellites and undersea cables serve different use cases. Cables are great for high bandwidth communications between fixed points but they aren't very useful to mobile military forces and they can't be used for anything beyond communications. We don't have enough ships and patrol aircraft to realistically defend undersea cables outside the littorals.
Satellites can serve multiple purposes including communications, navigation, overhead imagery, signals intelligence, weather, etc. They are also vulnerable, but it's possible to launch replacements faster than repairing damaged cables.
Inofficially Europe is already at war, whether it wants to or not. Maybe someone needs to inofficially keep a close eye on those cables and take inofficial countermeasures against inofficial sabotage acts.
The exercise left for the reader is to choose two countries that are not adjacent,
and try to plot a path between them without crossing an undersea cable:
We are at war. The United States guided an ATACMS missile into Russian territory yesterday. Imagine the absurdity of if China put missiles on the Mexican border and guided them into missile storage facilities 186 miles inside the border.
> maritime law that allows any nation state to freely roam over important cables.
I'd like to see your version of maritime law that doesn't allow freely roaming over important cables. Your country's enemies would gladly drop cables totally encircling you and say "uh uh uh, important cables!" if you tried to leave your perimeter