Because you sent them the cryptos on a voluntary basis. If you made an error, you can nicely ask them back, but they can nicely refuse. There is no notion of property, who owns the keys owns the management of the coins
>If you made an error, you can nicely ask them back, but they can nicely refuse.
How can you not see that "nicely" refusing is against the law after you have been prosecuted? You might argue that if someone sends you money you don't want, you only have to send it back once they get a warrant by a court but that isn't the problem here.