Lawyers tend to be very conservative.
For instance, clients often ask them for an assessment of "the chance of X going through". While clients can make it clear (in writing) that lawyers will not be held legally liable for giving "pure advice", lawyers often still refuse to give any guidance (even when they clearly do have one in mind).
This can be inefficient because clients often need to rely on imperfect expert assessments to make judgments.
What make lawyers so conservative? The "obvious" answer is that they do not want be sued. However, the same should apply to consultants, but consultants are much less conservative. Further, this shouldn't explain why lawyers are so conservative even if clients make clear that they cannot be held liable (assuming that such client statements are legally binding).
Given this, one more possibility is that this is purely due to the legal sophistication of lawyers. That is, even consultants should also be afraid to be sued, they failed to avoid it due to not being very sensitive about legal matters.