In addition, Arsenal is a team that does not change managers often. They tend to keep one manager for a long time and this allows Arteta to be retained even if he fails to win the Premier League title. Arsenal is very different from Chelsea, Tottenham or Manchester United, meaning they tend to give the same manager a chance to try his best.
Yes, Arteta was appointed as Arsenal's coach since 22 Dec 2019 and his contract ends until 30 June 2027, not to mention if there is a contract extension. So yes, Arteta already understands Arsenal's characteristics and needs very well. It's just that, unfortunately, Arsenal has only won a few trophies with Arteta, but Arsenal still keeps this coach.