That's how they clean out their customers' (I nearly said "victims' ") accounts.
These are counterparty market-makers, not genuine brokers: they're incentivized for their "customers" to lose.
Governments and regulators are very gradually clamping down on such high leverage - eventually it will doubtless be a thing of the past.
In the US it's now limited by law to 1:50, and in Europe they're discussing/recommending a 1:30 maximum.
High leverage in itself isn't dangerous in experienced hands, but the reality is that it tends to be used by the aspiring traders with the least experience and understanding, the most unrealistic expectations, and a gambling mentality, many of whom typically don't even appreciate the difference between a genuine broker and a counterparty, and what it signifies. In practice, there's a very high correlation in the industry between account leverage-levels and account blow-ups. These are "brokers" highly skilled at marketing, who know exactly how to attract the customers they want (ridiculously high leverage, gimmicks, deposit bonuses, competitions, etc. etc.), on whose persistent trading failures their own business model rests.