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Why blog is the wrong question. It is why publish?
The internet is about publishing content. Some you can pull in and scale with api's (api is a way to pull in feeds of data like IDX or other information) and such. Some you cannot. If you can pull it in, so can someone else.
So the big diferrentiator is your editorialized opinion. Your view. Your take on things.
It is what makes your site unique compared to all the other me toos or commodities out in the marketplace.