Committee member Albert Aribaud opened their campaign saying:
Worldcons are an old tradition. But in 75 years of history, none has ever come to France.
Today, we feel it is time to correct this oversight and to write a new page in the history of world SF.
Their FAQ says the new initiative was put together in late August by Albert Aribaud, Sybille Marchetto, Alex Garcia, Patrick Moreau, Georges Bormand, Alain Jardy, René Walling, Jean-Louis Trudel, Jean-Marc Lofficier, Benoît Robin.
It supersedes the Paris bid publicized at Loncon 3, which suffered because only two UK fans were there in support after its four French members got called away by a variety of work and personal reasons. That bid committee dropped out shortly after Loncon.
The FAQ also explains they are staying with 2023 partly to allow more lead time, but also because if they pursued a 2021 Worldcon it would be voted for at the 2019 Worldcon. Dublin currently is the only bidder for 2019, and that might bring into play the rule requiring at least 800 km between the Worldcon site administering the vote and any city being voted upon. They say: “Since Paris would be the most likely venue for a Worldcon in France and that the Dublin-Paris distance is slightly under 800 km, it could be a point of dissent.”
They have also ruled out 2022:
There already is a very strong American contender (Chicago) for that year which a first-time bidder would be quite unlikely to beat. Considering the amount of work that goes into a bid, it just makes more sense to pick a date that offers better odds for winning.
Worldcon In France is a pending non-profit association.