Hello There!!! This is my first visit here... Well friend I think you are using those theme which is designed be the professional developer of WordPress organization and you know very well this a huge organization and obviously they use their website name at the bottom of the website theme in order to promote their products worldwide. You will always find a brand name of any company or organization.
Therefore it would be better for you to download nulled WordPress theme from http://nulledwp.com/category/wordpress_themes/
. While using the theme you can change and modify each and every part of the website theme without much effort.