The reason we have banking to this day is, the bankers of the Middle Ages did their due diligence, continuing to audit the businesses to which money had been lent. The practice juiced growth, which increased incomes, changed the ways in which livings were earned, and of course led to some measure of control (ahem) over the monarchs both grand and mean. Whatever was good for business was good for the bankers, and for the overall economy, so there was a check on otherwise unfettered absolutism.
The politicians attach themselves to anything that has money in it like leaches.