The discouragement probably had to do with the stigma attached to "hidden variables" after the Einstein-Bohr debates, see Pinch, The hidden variables controversy in quantum physics for some social context. Quoting Jauch (1973):
"...the discussions which surround the quest for hidden variables in quantum mechanics have, on both sides of the camp, often been conducted in a spirit of aggressiveness which resembles more the defence of orthodoxy of one ideology than a spirit of scientific objectivity."
For a while, they were considered ruled out by von Neumann's 'no hidden variables' theorem. They weren't, as Bohm and Bell showed. But, as Pinch writes:
"Much of the ‘heat’ generated by the hidden variables controversy can, I think, be traced to the extraordinary faith which some people placed in von Neumann’s arguments. Clearly, hidden-variable theorists were likely to interpret this as a blank refusal to believe, based on prejudice and dogma, while the establishment, on the other hand, was likely to see the refusal to accept von Neumann’s arguments (which after all had in turn never been shown to be invalid) as irresponsible and likely to open once more the doors to pointless speculation over the foundations of the
theory."
In 1966 Bell showed that von Neuman's proof was essentially circular, in it hidden variables were ruled out not by quantum mechanics but by his extra assumption that was not even reasonable. This "notorious gap in von Neumann’s argument" is now broadly recognized, see Mermin, Homer Nodded: Von Neumann’s Surprising Oversight, but the attitudes were already set and slow to shift. Even those who did not rely on it perceived the search for hidden variables as akin to the futile search for aether, and Bohmian mechanics still has a bad reputation even now. As Pinch puts it:"After the earlier battles to get the Copenhagen interpretation
accepted at the famed Solvay congresses in
the 1920s it was hardly likely that the physics elite would let the foundations of the theory be undermined by the post-war generation of physicists."
But in 1970s hidden variables still were the only approach to "normalizing" (in Einstein's sense) quantum non-locality, and Bell saw it that way. Objective collapse theories that he eventually switched to only appeared in 1980s. In Bernstein's Quantum Profiles he is quoted as saying:
"I feel that Einstein’s intellectual superiority over Bohr, in this instance, was enormous; a vast gulf between the man who saw clearly what was
needed, and the obscurantist... What worried me then was how to get rid of that division [between classical and quantum behavior]. I was looking for some reformulation of the theory that would permit its elimination. It was clear to me then that the hidden-variable approach would be one such formulation. If you gave definite properties — ‘hidden variables’ — to the elementary quantum particles, you don’t have to be concerned that the classical apparatus has definite properties. Everything has definite properties. It is just that they are more under our control for big things than for little things. It was clear to me that that was one line of possible development."
