WordPress.com is a multiuser blogging platform. There are over 600,000 of us blogging on this platform and to keep it secure forms are not permitted. I could hack a single form and obtain access to all the other blogs.
However, do not despair. There’s a simple solution available. You can go to wordpress.org and download a free theme and import the contents of your wordpress.com blog into it because http://wordpress.org runs on different software.