I believe most marriages don't last long for two reasons:

1. People rush into it not well-prepared, believing marriage is all fairytale like its portrayed in movies.

When the challenges come up, they are unable to cope hence, the breakup.

1. For selfish reasons. People rush into marriage for their personal or selfish gains and not because they have genuine love for their partner.

If for any reason, the benefit they're getting disappears, it becomes almost impossible to stick around.