Extracting data from JSONB column

I suggest looking into the operator precedence table (highest to lowest):

The JSON field extraction operator (->) falls into the category of any other operator, which comes after the subtraction/deletion of keys (-). So the initial expression is equivalent to this:

feat -> ('properties' - ('{highway,surface,tracktype,maxwidth}'::text[]))

A cast works since it has higher precedence than both of the other operators. Also, just brackets work:

SELECT 
  (feat -> 'properties') - '{highway,surface,tracktype,maxwidth}'::text[]
FROM (
  SELECT
    jsonbarrayelements(fc->'features') As feat 
  FROM data
) as f;