It's just toooo Hard
(backwards flight)
hmmmmmm what is the actual useful purpose for flying backwards????
(backward Auto from a good height to eventually get 65knots fwd ASI- OK)
But....If there isn't a good reason for flying low level at high speeds with ETL+ in reverse, bar challenging one's (superior?) Skills
then.....otherwise Airmanship dictates taking the Safest, or at least more Safer options, thus avoiding that area of flight; as it has additional risks, challenges & (potential) dangers
OmOmOm