The only answer is price in France, that's it. Time-wise that's about the same, trains are very fast and planes have a longer travel from the city center so that's even it out.
Any source on this or it's just your assumption that trains are faster and more reliable? I doubt that would be the case in France especially when it comes to trains.
Faster yes.
Reliable certainly not.
On time even worse.
If you're thinking about strikes, airplanes also have their fair share of strikes in France.
If you’re lucky, the train conductors and the air traffic controllers won’t be on strike at the same time though!