Ask HN: Why do web sites not place the cursor for input?

To their credit, Microsoft puts the cursor in the text field ready for me to type in my authenticator code. Most web sites I've found, do not. So I look up with my shiny new code, ready to start typing, realize I need to move my hand to the mouse, place the cursor into the field then there's a 50% change I've forgotten the code and have to look back at my phone.