I previously did not have and was not seeking to acquire the downloadable maps for halo 3, but just now when I was looking in the marketplace I noticed that the map packs were free? Did something happen that I was not aware of that made them free? Because as far as I knew you needed to actually spend money to buy them. I am not complaining, I am happy to get them for free 
but I was just curious. Any clarification would be appreciated!
All Halo maps packs were recently made free with the announcement that Halo: CEA, Halo 3, Halo 3: ODST and Halo 4 will become backwards compatible titles later this year
https://www.halowaypoint.com/en-us/news/halo-summer-celebration
Great! Thanks!