Before the current canon, there were a few Wookiee Jedi, like Lowbacca (very original name, I know) until George Lucas himself made it a mandate that there would be no more Wookiee Jedi.
According to Lucasfilm’s Pablo Hidalgo, it was after concept artist Derek Thompson suggested a Wookiee Jedi for “Revenge of the Sith” that Lucas decided to roll back on the concept. This likely happened as a way to prevent an explosion of more Wookiee Jedi while Lucas developed the planet of Kashyyyk for the last of the prequel movies. Eventually, he went back on this and decided Wookiee Jedi were rare rather than existing, which is why the droid Huyang comments on how rare Gungi is among the Jedi ranks.
This is far from the first time Lucas has gone back on one of his own mandates or ideas for the sake of a cool moment or character. There’s the time he suddenly decided Maul wasn’t dead anymore, despite being vehemently opposed to the idea for years before that. Like with Maul’s return, “Star Wars” is better off with Gungi in it, because the idea of a Wookiee Jedi — especially that being rare — is just too fascinating to pass up.