B018 doesn't trigger for useless expressions involving multiple variables

I recently ran into the following bug and was surprised it wasn't flagged by B018:

def some_funcion(a, b, c, d):
    result = a * b
    +c * d

    return result

that should have been

def some_funcion(a, b, c, d):
    result = (
        a * b
        + c * d
    )

    return result

It looks like B018 doesn't trigger for expressions containing multiple variables.

Here's some examples:

a * b     # doesn't trigger B018
+a * b    # doesn't trigger B018
+1 * 2    # doesn't trigger B018
-1 * 2    # doesn't trigger B018
1 * 2 + 3 # doesn't trigger B018
a + 1     # doesn't trigger B018
a         # triggers B018
(a, b)    # triggers B018
1         # triggers B018
+1        # triggers B018
-1        # triggers B018

Versions I'm using:

python version 3.10.13
flake8 version 7.0.0
flake8-bugbear version 23.12.2
ruff version 0.1.13

Start by locating the B018 implementation and its existing tests, then reproduce the listed expressions with the reported Python, flake8-bugbear, and Ruff versions. Extend the B018 behavior so the multi-variable expressions described in the issue are flagged, and verify the existing triggering examples remain covered.