Why Japan could pressure French colonies

Was French naval weakness part of why Japan had such freedom of action in Vichy colonies?

Yes. France lacked the naval strength to protect a dispersed empire independently once British support was unavailable.

Wartime Japanese pressure followed from a force structure created in the interwar period. France needed its fleet to balance Italy in the Mediterranean, leaving insufficient strength to protect distant colonies at the same time. British planning also depended on France neutralising much of Italy's fleet so the Royal Navy could divide attention between Europe and the Far East. When Britain could not or would not defend French possessions, those colonies became highly vulnerable. A treaty-era regional balance thus produced global consequences two decades later.