Why not an axemage, or a macemage, or glave-guissarmemage?
PF calls it magus to indicate it's not locked into any specific weapon.
Why "Rogue" and not "Thief" or "Blaggard" or "Burglar" or "Crook" or "Assassin"?
Why "Fighter" and not "Warrior" or "Soldier" or "Battler" or "Hero" or "Trooper"?
Why "Wizard" and not "Mage" or "Magus" or "Sorcerer" or "Magician" or "Thaumaturge" or "Warlock"?
Why "Paladin"? The Palatine hill doesn't exist anywhere except in Rome, and the knights of the pious Big Chuck (Charlemagne) certainly didn't exist, so surely that
should not be called by such a hyperspecific, historically-bound term,
particularly since the use of "Paladin" was always reserved for a monarch's closest personal guard. Yet D&D not only coined the term for "knight dedicated to a deity", it has effectively been the
sole reason the term "Paladin" continues to exist at all in modern fantasy fiction, and almost completely displaced the old "closest retinue of a king" meaning. Like it would genuinely be the equivalent of calling the martial leader-of-men class "Praetorian" instead of Warlord; why should any world
except Earth have any concept of a "Praetorian"?
For that matter, why "Eldritch Knight"? Most Eldritch Knights are not knights of any kind--they swear no oaths and have no liege-lord who calls them up.
Surely they should've been called "Eldritch Soldier"
but then they aren't soldiers fighting in war, they're mercenaries, so it should have been etc., etc.
Names come to us from a lot of sources. Some of them are way overly specific but kept for legacy reasons. Consider that many Bards will not be bards in any sense (neither performers nor royal chronicler-satirist-historians), many Rogues will not be rogues (and may in fact be entirely upstanding, law-abiding citizens--Sherlock Holmes makes sense as a high-Int Rogue, for example), many Druids will not be priests of a specific cultural group, etc.
The PF Magus is a horribly fiddly class.
An entirely subjective judgment that in no way invalidates the
archetype behind the class.