When you click "edit" to start editing an existing statement, the focus is not moved to the input field.

If you want to edit the value, you have to first click into the input field or tab from the beginning of the page to the input field, so focusing the field would remove a step in that case. If you want to edit something else (qualifiers or references), it would be easier to tab from the input field than from the beginning of the page when using the keyboard and it should make no difference when using the mouse.

This would also be more consistent with the "add" buttons which do already focus the first input field.