The Samknows website shows Tamworth exchange as having FTTC available in "some areas". When BT install FTTC they activate some cabinets but not always all. The choice is determined by them based on economic, technical, planning and practical issues which they do not explain so your guess as to why one area gets it and another doesn't is about all you have to go on. In some areas they have said they will come back and fill in some of the gaps so it may happen later.
The best place to get accurate information about your line is at the BT Wholesale Availability checker http://www.btwholesale.com/includes/adsl/main.html. You can enter your number if you already have a BT line or postcode if you don't. If FTTC is planned it will show up a few months before it goes live if you don't see it there are no current plans to upgrade your cabinet. Sorry but apart from starting a local campaign there is not much else you can do.