Why the pattern to power down

You really don't have a question here, but since you seem new I will not down vote or attempt to close it because I think I can guess at it.

I assume you want to know why this occurs, it is simple security.

The "fix" is just as easy, hold down the power button and continue to hold for about 15-30 seconds and the device should hard reboot (essentially like pressing the RESET button on your computer).

You will need to perform the factory reset via recovery, so know the key combo and be ready to hold it immediately at restart, it might take a few tries to get the timing right.

Remember you will likely need the username and password of the Google account that resides on this device, or the reset will not matter and you will be locked in FRP.