Why are so many US Hollywood films made in the state of Georgia?
While film in the United States as an audience artform started in New York it moved to Los Angeles for the stated reason of longer and sunnier days.  Another part of the story was a patent dispute in 1898 between Thomas Edison and his patent for the Kinetograph.  Edison stated that he effectively had a say in how films were made and wanted royalties for their use.  Moving from New York near where Edison was based to Los Angeles was a simple way to grow the industry and distance themselves from a patent war.  

This mobility at the start of the modern film era due to costs continued through the 1960's and 1970's with westerns being shot in Spain.  The 1980's and 1990's continued this trend primarily shooting in Canada or Mexico.  At the turn of the century state legislators in the United States started provided steep tax rebates.  The practical outworking of this is studios are encouraged to hire local talent and use local services when producing their film.  The ratios for these rebates is fairly complicated and have created a new industry of tax professionals serving the film industry.

So then why Georgia?  Georgia currently provides one of the highest incentive structures at 20% with minimal restrictions on talent and a very low minimum budget of $500,000.