This isn't so much about France's network being Paris-centric, but the massive natural barrier to transport that is the Pyrenees.

The problem us that Spain uses a different track gauge than France, so connecting the countries is difficult.

Fun fact from Wikipedia:

> Since the beginning of the 1990s new high-speed passenger lines in Spain have been built to the international standard gauge of 1,435 mm (4 ft 8+1⁄2 in), to allow these lines to link to the European high-speed network.

(...)

> In general the interface between the two gauges in Spain is dealt with by means of gauge-changing installations, which can adjust the gauge of appropriately designed wheelsets on the move.

I didn't know that!

I believe I’ve read this was also due to Iberian gauge high speed rail technology not really being existent at the time Spain started building HSR in a hurry for Expo ‘92? in Sevilla, and they’ve continued using standard gauge for it (to the benefit of the link with France).

However the huge investment in HSR (longest network after China, but low utilization), has also come at the cost of the local and regional train network (which still use broad gauge, yes there are gauge changing trains, but the broad gauge network is languishing).

The Talgo train with adjustable track gauges has been connecting france/spain for quite a while, but it is by no means designed for long-distance, high-speed travel so Spain kind of had to resort to switching to standard gauge which is also what other important neighbouring countries and possible destinations use (France, Germany, parts of Switzerland , Benelux, Italy).