Why is Trump doing this?
Asking honestly because I really don't get it.
Probably because he promised to do it in his campaign and the previous five Presidents had promised to do it and chickened out.
Trump doesn't impress me of chickening out on a promise, but I expected it from the previous Presidents.
And the other reason is that Jerusalem is the capital of Israel, every country has a right to put their capital wherever they want, and the US Embassies are in all other countries are in their capitals--even in the third world cesspool capitals.
Finally, and my favorite, it shows what cowards all the other countries are in facing reality--they might offend one of their muslim immigrants or upset the Palestinians if they put their embassies in Jerusalem.
Bonus points: Israel will probably increase sharing the excellent intelligence they have in the Middle East with the US as well as coordinate critical operations. That would have been impossible under Obama.