This is one of the big mysteries of the film. Why is Luke in seclusion? Why hasn't he trained anyone?
My take on it is that he has trained some Jedi before going into hiding. Maz Kanata for one, as she seems to have force training of some sort judging by her dialogue. Where would she have got that from if not from Luke?
Also Han says "They're real" referring to the Jedi. Not they were real, but they ARE. My guess is that there are quite a few former pupils of Luke's scattered about the galaxy, having gone into seclusion because of...something.
I have picked up several fragments of rumors but they could indicate a pattern:
THE EMPIRE STRIKES BACK: one theory that sounds credible to me was that Dagobah and in particular the cave with the man made structure inside used to be a Dark Lord's place and Yoda's presence somewhat counter-balanced the dark energy which also made him invisible to the Emperor and Vader
REBELS: Kanan thinks the temple on Lothal is of Jedi origin, but I think he could be mistaken because architecture and hieroglyphs suggest quite the opposite (according to Ralph McQuarrie)
THE FORCE AWAKENS: Somewhere it had been mentioned that Luke is doing something similar as Yoda did in ESB.
So, are the Jedi avoiding a confrontation with the new Dark Lords, let "mundanes" handle it first and just make sure that powerful Sith artefacts don't fall into the wrong hands?
Just my two 0.02 $
P.S. Phasma looks like a Cylon warrior from BSG 1978.