I know that ITV is based in Bristol which of course has by far the biggest population, but even allowing for that Wiltshire always plays second fiddle to the news from Bristol, Gloucestershire, and Somerset.
Remember that Swindon is easily the second largest population, and there are many towns in West Wiltshire particularly close together that also have a combined largish population.
I don't wish to be over-critical, but for me ITV News West Country is not very good value if you happen to live westward of Bath.
BBC Bristol is only marginally better in my opinion.