I've written about Hanover a few times in the past -- the very short answer to your question is that Hanover was not a British possession or necessarily of concern to Parliament. The British monarchs were also electors of Hanover; but those two legally distinct people just happened to occupy the same body.

https://www.reddit.com/r/AskHistorians/comments/3jbpyk/britains_role_in_running_hannover/

https://www.reddit.com/r/AskHistorians/comments/401lb1/why_wasnt_hanover_incorporated_into_the_uk/