because counterparty market-making forex “brokers” offering high leverage are not reliably regulated, simply because the UK, European, Australian and American regulators (for very good reasons) don’t allow such “brokers” to offer high leverage
it’s really very, very simple: if you see a “broker” offering high leverage then you already know that they are not regulated by a proper regulator, and therefore not trustworthy - because the two things are, by definition, mutually exclusive
be aware that brokerages choose whether and by whom to be regulated
in Australia (just to take one example) there are brokers regulated by ASIC (they don’t offer high leverage and are not allowed to), and other brokers not regulated by ASIC (some of whom offer high leverage), but you can be 100% certain that if an Australian brokerage offers you a high-leverage account, then that account is not regulated by ASIC and is not one with which you should open an account - there’s nothing difficult to understand, here, as long as you avoid the mistake of assuming that because a brokerage is based in a country which has a reliable regulator available that that brokerage has chosen to be regulated by that regulator - many have made the opposite choice, and their reasons for having done so are not too hard to understand! 