I've been at my current company for over a decade. The company has changed a lot over the years, going from a large public company when I joined, to private, back to public again recently.

The reasons I stayed are simple: I've learned a tonne, changed roles and responsibilities, interacted with many interesting characters, and continue to grow personally. No matter the tenure, if you aren't being challenged then your boredom will affect your performance.

Create new challenges that solve problems within your organization, and if that doesn't work by all means strike out for greener pastures.

Best of luck.