Money today is more valuable than money tomorrow. Tech seems to have been a curious exception as it was in the 2000 bubble.
Not to mention, Facebook is quite the pioneer in tech. React is one of the most used front end libraries and the community around it is super positive.
Then there's VR and their progress in 360 video. The list really goes on with Facebook.
Twitter on the other hand, it's not that they have failed, but probably that they were aiming a bit too high. Investors were likely expecting another Facebook, but Twitter is never going to become that, because it's not perceived as a fundamental part of people's digital lives. Everyone has a Facebook account, but only some use Twitter.