Sometimes those reasons are a bit dumb. Many times it's called "thinking for the future" or something, when it couldn't be clearer the realm just doesn't have the guts to make that enemy realm's characters/players hate them for a long time. Of course it's sometimes interesting to wonder just how long term some players think. BM's been going on for what, 8 years? That's already a pretty long time, but just how long do they want their plans to take? I wouldn't place any bets on any 10 year plans because you're probably better off investing in some stocks in the hopes that the economy gets better in 10 years. Maybe 5 year plans are a bit more credible, but even then, BM would be 13 years or so. That's a pretty long time for a specialty online game.
The other factor is always fun. As a player I have some responsibility to other players in terms of providing fun. This counts for my enemies as well as my realm mates. Not saying that means I won't destroy realms, I'm certainly all for it, just that I do consider the OOC aspect of such things as well.
