Why are some forms limited in the types of fields I can implement into them?

Why are some forms limited in the types of fields I can implement into them?

For instance.. Between two similar forms on my app on the left side there are almost twice as many field types I can choose from.. I am editing a form and want to implement a 'file upload' field into it but there isn't even an option of the left-hand side to drag a file uploader onto the form. How do I get around this?