It is not frozen, but if most of the platform's reserves are in its own currency, this means that the clients' money is on thin air. Just like what happened with FTX they took bitcoins from customers and calculated that they had millions of reserves in the form of their own currency which they later failed to sell.
YouTube and Google have accurate details about how this platform collapsed but as a general rule, stay away from any platform with a large reserve of their own coins.
This picture explains what I'm trying to say.
Source https://beincrypto.com/learn/ftx-collapse-explained/
You have a valid point here but BGB only constitute 30.33% of the reserve which seems a bit healthy from your POV. Beside, its normal to have a sizeable reserve in exchange token cos most of them have utilities on the platform which obviously lead to increase in the demand. BNB is used for lanchpool, MX is used for their kickstarter and launchpad event while BGB has similar utilities on Bitget which includes Launchpool, launchpad and their super airdrop.
FTX saga was purely mismanagement of users fund owing to lack of transparency and accountability. Apart from the PoR few exchanges, notably Bitget, Binance and OKX have been working hard to ensure the safety of user assets by launching customer protection fund as another security layer guaranteeing the safety of users assets.
I guess all these efforts should be appreciated imho taking into cognizance the high risk of losing assets in this space.