If you close public transport 5~10km around the protests, there wouldn't be much public transport operating in Paris. Rather there were a handful of closed subway stations, around where the protests were (like Etoile was closed, but not the closest stations). I understand the idea, a stampede in subway corridors would have caused casualties.
I think you might be referring to the later protests. Before the gov. "concessions", they shut down basically a quarter of Paris.
Even without using public transportation, you could try to walk from the Louvre to Etoile for instance and get blocked as soon as at Concorde by police barricades. We went to Chatelet/Les Halles during the whole thing, and you would see protesters preparing their masks, helmets etc. and planning their path to the main place to avoid hitting the main police blocks.
