Inertia.
Personal administration stuff like this feels like a massive ball ache to get stuck into for many, and I include myself in that.
Whether it's car breakdown cover, buildings and contents insurance or the mortgage, it feels easier to just let things renew or persist without checking the...
Circumstances change though, don't they? People lose jobs, have hours cut or other outgoings arise. What may have been seen as a perfectly manageable increase when a mortgage was taken out, may not be quite the same by the time it happens.