Coop is able to communicate with his past self. So why does he not provide the correct data about which planet is the viable one, saving lives and resources?
Cooper cannot change the past.
Once his future self, who entered the tesseract from the black hole, accepts that he can't change the past, he then understands that he can make sure that the lives and resources were not sacrificed in vain and so moves on to hatching his plan to save mankind.
This is explained in the discussion with Coop and TARS:
TARS: Cooper, they didn't bring us here to change the past.
Cooper: Say that again.
TARS: They didn't bring us here to change the past.
Cooper: But they didn't bring us here at all. We brought ourselves. TARS, give me the coordinates for NASA, in binary.
TARS: In binary, roger, feeding data. [Cooper creates the binary lines in the dust on Murphy's bedroom floor]
Murph: It's not a ghost... it's gravity.
Cooper: Don't you get it yet, TARS? I brought myself here! We're here to communicate with the three-dimensional world! We're the bridge! I thought they chose me. But they didn't choose me, they chose her!
This is an example of a causal loop - where, for instance, a time traveller travels back in time to instigate a series of events, which may include events leading up to them going back in time to instigate the events.
In this case, future Cooper interacts with the dust in order to send Murph the coordinates for NASA, thus leading up to the events of the movie. In a hypothetical scenario, had he not done this, Cooper would not have joined the mission and he would not be able to travel back in time to do this in the first place. You could say that he has to do this - someone has to manipulate the dust from the future to send Cooper on his mission, otherwise all the events we've seen wouldn't happen. And we know that they have to happen because they did happen, so they can't not happen.
As to why Cooper doesn't just send the location of the correct planet etc. - same reason. Events have already played out in the past. There is only one past - Cooper can't change it and cheat.