That explains why they had some typical celtic things like druids.
[1] https://acoup.blog/2023/05/12/collections-who-were-the-celts...
It's an exonym, i.e. it's not how the celts living in Gaul would call themselves.
There are two origins of the word that are likely to cave coexisted in a "convergent etymology"
1. The name of an ancient Celtic tribe (one of many) sounded like "galatai" to ancient Greeks and it sounded about right because of the the white skin (either fair skin or white paint). So in this case it ultimately stems from a Celtic word.
2. The old Germanic word "walhaz" meant something like "foreign" or "Roman". That originated many names for former roman territories when Germanic people encountered them. (Similar word for Slavic). That left a lot of names like "Wales/welch", "Wallachia", "vlachi". This word went through a sound change when adopted in romance languages similar to how other words like "werra" - > "g(u)err(a|e)", "Ward" - "g(u)ard" ...
The regular sound changes in languages betray the coexistence of these two etymologies at different times and phases of the Evolution of the romance languages and french in particular.
The latin "g" sound evolved into "j" (gamba -> jambe) so one our think that if the word "Gallia" was available from the latin substrate it would have transformed into "Jallia" and in fact it was! As attested by place names like La Jaille-Yvon and Saint-Mars-la-Jaille.
This reveals how the modern french name "gaule" likely stems from the second etymology (the German origin).
That said, languages are rarely let evolve naturally. There is plenty of people who studied languages and kept latin alive for centuries and it's also quite possible that the version with the "g" sound has been also kept reinforced because of the relationship with the classic texts (Gallia est omnis divisa in partes tres)
Or Franken (i.e. parts of Bavaria) that they're Bavarian.
Or English that many of them are part French nowadays (think Normans).
Or ...
History is messy. People are messy. Mostly vengefully so unfortunately. This is why we can't have nice things.
Freud called this the “narcissism of small differences” (https://en.m.wikipedia.org/wiki/Narcissism_of_small_differen...).
People of Frankish descent are mainly found in the Rhinelands, which does include a bit of France, but is mostly located in modern Germany.
But OTOH the name "France" is unequivocally Frankish (Germanic) and thus not something that Obelix, a Gaul from ~2070 years, ago would identify with.
An obelisk is a type of pillar from Ancient Egypt.
But Asterix and Obelix are of course named after asterisks and obelisks. It's part of the joke.
(I always found that cool)