Many possible reasons...

1) The plane had more done than just WiFi. C checks take 3 weeks, D checks around 2 months
2) If on top they were waiting for some pieces or certification of something that they installed, the plane is grounded for longer
3) Summer in France... even less people actually do work. Throw in a bit of small striking here and there, etc, and things just take longer

I am not sure in how many cases they simply take a plane, park it in the garage, install Starlink and be done.