One of the biggest costs with shooting on location is paying compensation to those affected, cops for security, permits, hell, lawyers writing up contracts for people to sign, agreements for a business to be shut down for a day, or 3.
CGI isn't surprising though as others have mentioned its not really "cgi" in as far as what we generally accept CGI to be.
TO a certain degree theres just SO much tv shot these days it would be ridiculous with every show trying to shoot its stuff on location in New York and LA, half the city would be shut down daily with 50 different shows all having 10 locations per episode every week.
THe by product of so many shows is again that, everywheres already been shot once, or 582 times, so why reshoot the location again when you can just merge the two images.
Its interesting to see a few examples I didn't know about, Episodes is apparently lazy as hell, if I was one of the writers on Episodes and didn't get to film it in LA I'd sue someone
To a certain degree its very not noticeable because, for the most part the location isn't particularly important so theres not a huge reason to be looking anywhere other than at the characters. Some shows do it painfully badly, White Collar did it through the beginning of series 2, I think Kelly from saved by the bell was having a kid or something, was clearly never in the same location as her husband and it was WOEFUL green screen merging them together in scenes, literally the worst green screen I've ever seen.
The Lotro stuff is interesting but, not particularly difficult, the only insane scene is the rotating around the table situation where they are making a heck of a lot of effort, more to prove they can do it than actually having to have a scene where the camera moves at that particular time. As in more like the special effects/set team complaining to Jackson they were bored and wanted a challenge, or jackson bet them they couldn't do it than the story being ruined if they couldn't move the camera in that one scene.