Because position hoarding only adds to the sentiments that the realm is ruled by a small clique and that everyone else is obsolete and/or expendable. One complaint I've heard once too often is 'Why would I bother trying to get promoted, the top spots are always passed around between the same people anyway?'
Because these people might just be hogging the titles while waiting for someone who gives a damn to show up. I've taken titles on many occasions without really wanting them but because the only people who campaigned, if any, were either completely incompetent or had obvious seditious ambitions. I usually later stepped down whenever a worthy candidate presented itself.
Another thing might be that one *wants* some of the titles while at the same time not finding anyone for the rest. For example, I might want to be ruler and/or duke in order to be "the man" in the realm, without any ambition for the other title, but if the only candidate for the banker position is from a family known to repeatedly steal gold from the realm or the only general candidate a person who was marshal for a long period but never bothered giving orders (or gave really bad ones), then you may be inclined to take these extra positions in addition to your favored positions.
There are so many realms in BM that work so differently... If you don't like how power is spread in your realm, nothing is stopping you from joining one of these realms that don't allow more than 1 title per person.
