Suggest tactic missing a suggestion

Stream: general

[Michael Stoll]

Consider this:

import algebra.group.basic
import data.real.basic
import tactic.suggest

-- this produces only a list of unhelpful too general things:
-- Try this: refine eq.symm _
-- Try this: refine eq_comm.mp _
-- Try this: refine eq_comm.mpr _
-- Try this: refine inv_inj.mp _  etc.
example (a b : ℝ) : a + (b - a) = b := by suggest

-- However, we have
example (a b : ℝ) : a + (b - a) = b := add_sub_cancel'_right a b

Why does suggestnot find the exact match?