To protect themselves against consumer fraud and protect their customers from malicious access where a fraudster logs in and then tries to withdraw funds.

To protect themselves against consumer fraud and protect their customers from malicious access where a fraudster logs in and then tries to withdraw funds.

Edit : Most firms won't disclose this for safety reasons but I did find reference in the Robin hood FAQs: https://support.robinhood.com/hc/en-us/articles/208650296-Transfers-to-Your-Bank-Withdrawals-