West Berlin was a political enclave in DDR. ~150 km from the inner German border [1]. Just outside Berlin is pretty much ex-DDR territory. At the same time Berlin does have quite a strong foreign community and high migration, lately negative for Germans and positive for other ethnic groups [2]. It is the second largest city (by population) in Europe after London with much lower living costs [3]. Also Daimler and BMW have strong presence in Berlin. Those factors may have influenced the Tesla's decision a lot.

[1] https://en.wikipedia.org/wiki/Inner_German_border

[2] https://www.statistik-berlin-brandenburg.de/produkte/kleines...

[3] https://teleport.org/compare/berlin-and-london/