The thing all those towns with styled main streets have in common is tourism. Not every town is a tourist attraction.
You know, this reminded me of something. On a trip a few years back to Australia, we rented a car and got out of the tourist land of Cairns. (My husband and I prefer to see the real countryside, real towns, etc.) The friend who was with us had been on 3 trips to Cairns, and was utterly shocked that the entire country didn`t look like the perfectly coordinated tourist aimed streets around the hotels.
Places that aim to attract tourists invest money into renovating to match the "image" they are trying to sell. It works great when there is income from tourism that can be both used to do this and which will potentially be increased by doing so.
But in the average town without any significant tourism? It would be an incredibly expensive and stressful endeavor. There would have to be some way to convince everyone to rebuild their buildings around the same time, or to surrender their land to make the area prettier. It`s not all that easy.
Personally, I hate the artificial tourist streets. I know someone personally who lost half their land and had their 200 year old building torn down...to be replaced by a "new" 200 year old style building that fit the main street image better than their original. All because their town was trying to call in tourists and decided that renovating the main street to fit the image was the best path to take. Now it all feels fake... But gets tourism.
The friend ended up quitting the family business that was what the tourism was supposed to be founded around and now the town has pulled in "travelling craftsmen" who are just students from the local university to pop out souvenirs.
I think that things would be better off looking better, but I don`t think that tearing down whole areas and replacing them with "better looking" buildings that make it hard to do anything other than run a tourism based business is the answer.