Plenty of people do that. I have a male friend who has been with the same girlfriend for 7+ years. Around the 5.5 year mark (before the pandemic hit), he told me that the relationship had peaked 2-3 years earlier. Why stick around a meandering and mediocre relationship now for 4+ years and counting.
A lot of relationships survive on inertia for many years. It is a royal pain to try to establish a new relationship. Lots of bad first dates, lots of ghosting, lots of swiping/
texting, lots of late nights in the bars, lots of meaningless social events such as singles mixers, etc. These are all things that happen to people when they try and find a relationship.