.
It's a combination of the factors already posted: Lack of moving with the market's trends, business rates and rent, being too big to easily adapt, taking too much notice of the share price, etc. It also matters who is at the helm of the business.
Comet and Jessops have gone the same way but I can't say I'm sorry. My Dorset market town has a very vibrant high street (actually 3 because of a 'T'-shape layout) and no big chain shop players.
There'll be other big chains going bust but I wonder how the empty shop properties will be dealt with. The landlords will have to learn to be less greedy - If that's possible! Did you know that a high proportion of retail property is owned by the Church!