Funny you should mention this query as I was pondering it earlier as well.
What I came up with is that Wall Street is really just a whole bunch of people. Most of whom have dedicated themselves to taking the path of least resistance, much like people do everywhere.
When their collective semi-consciousness begins noticing more frequent mention of Tesla and Elon in a positive light they jump on the bandwagon. More so because that appears to be what the crowd is doing. This stems from the fact that their analytical skills are finely honed for planning where to eat lunch and what to do next weekend, more than they are for sorting out facts and figures and all that hard stuff their job title might allude to.
Likely, they have also gotten some negative reinforcement over their careers in regard to past attempts at decision-making based upon their own skills (or lack thereof) and have migrated to the safer "follow the herd" strategy. This way, even if the herd is wrong, there is someone else to blame and they keep their jobs.
Or, maybe it is something else entirely. That is the way it goes with complex dynamic systems, particularly when people have a hand in them.
Where shall we have lunch?
Might I suggest Milliways?