There are a number of reasons. First and foremost though I just want to address a common misconception that Findom(me) =/= Prodom(me):

• Prodomme is what you would consider a stereotypical dungeon dominatrix. You are paying a professional for use of their time, space, and knowledge for bdsm services.

• Findom is short for Financial Domination. It involves a relationship where a submissive(almost exclusively male) gives money to a dominant(almost exclusively female) and generally involves elements of humiliation of some form for the act. The expectation is generally that you will be treated as a human ATM with a complete disregard for anything else.

It's frowned upon because it's extremely exploitative and violates a lot of mutual respect tenets of BDSM play. Typically it's used as an easy guise which is low hanging fruit for lazy sex workers and scammers trying to make a quick buck and can easily get out of hand quickly for a site that leaves it unchecked. It exists in the same vein as Sugar Daddy/Sugar Baby play, but without even pretending to have a relationship beyond financial gain.