If Kipchoge tries to break the WR in Berlin, I believe that will be the first time he has actually tried to do that. Only his prior race in Berlin could even potentially have been considered a WR attempt by Kipchoge. He races to win, and only races highly competitive races, so the times have come. The non-majors aren't competitive and neither is Chicago anymore (not as deep as the other majors). London has had some great times, but it is not as fast as Chicago or Berlin by any means (having run all three myself). It is not even remotely pancake flat like Berlin. London gets the times because it is by far the most competitive.
If Kipchoge had moved up to the marathon after the 2008 Olympics and medaled in 2012 his career, extending from 2003 to now, would put him in the discussion as greatest ever distance runner (he is already the GOAT in the marathon), but moving up maybe a little later than that left a good sized hole in the middle there.