This has been asked a few times, maybe someone more knowledgeable will have something more to say, but to sate your curiosity here are a few links to various other answers.

/u/thejukeboxhero : https://www.reddit.com/r/AskHistorians/comments/445ak0/what_is_the_primary_reason_that_the_visigoths/cznl9p3/

/u/cptbuck : https://www.reddit.com/r/AskHistorians/comments/3rb6y5/a_small_splinter_group_of_the_muslim_army_crossed/

/u/bitparity : https://www.reddit.com/r/AskHistorians/comments/1uce2a/how_viable_was_an_umayyad_occupation_of_france/

edit: to add the first link from faqs and added pings like the bot told me haha