Because they want to simplify every job into a single 2 minute buff window, rather than letting players experiment and giving certain jobs more synergy than others. Ninja was awesome to have in a party, it allowed jobs to shine that have trashy 2 minute skills whilst also rewarding the jobs that do have good 2 minute skills. It paired well with Mch and Smn. Since they have solid 1 minute windows. It was a nice thing that partys could play around and be rewarded for but instead, we have to have 2 minute boring burst windows because god forbid players have creativity and be rewarded for planning in end game content.