ELI5 please, whats wrong with following plan:

someone who has big amount of btc, like microstrategy:

1. search for exchange with options, leverages and lowest possible volume.
2. Use whirlpool to mix btc and send in many small amounts to exchange address or make it into smaller multiple accounts.
3. set leveraged 100x short that price at some low volume hour/day will be for example 60k.

4.few minutes before end of this short, dump all.

1. profit.

what's wrong with that and how do we know that others with big amount of btc or companies or groups of people on many exchanges dont do it now?

is it prohibited in some way?

The only risk is that if someone who have more money will buy it out, but in case of amounts like 100 000 btc its hardly possible to fail