This is because everyone who trade FX and is not an institution, lose money. This is also why no hedge fund trade FX.
Most of IB's volume come from hedge funds that have less than 100m$ in AUM. So they don't care too much about people who open FX accoutns for 10k or 25k or whatever.
The FX business model has always been:
- Get 10k accounts
- Don't book the client's trade, essentially if the client buys, the broker sells.
- 95% of the traders lose 95% of their money in less than 95 days.
- Broker makes 10k.
If you're thinking STP like IB does, how much money will you make on 10k$ fx account.... 100$ over 2 years? forget about it. So they don't want to overhead of compliance and possible risk of clients being angry because they lost money, when they have the hedge fund business.