@JessTheUnstill My cynical suspicion is that much like more police create more crime, SWAT teams create excuses to use them for internal reasons. If you have a SWAT team sitting around not doing anything, do they really need all of that budget money? So SWAT teams are motivated to find ways to get used, the more the better (for their budget and prestige).
(Plus this isn't just police, there's a whole pressure on government as a whole to be 'efficient', which often means no idle resources.)