Southgate usually prefers someone who's playing in the hole behind the either Vardy/Kane. And no, Benzema doesn't play as an out-and-out striker for Real Madrid but more of a SS/F9 or even as a CAM. Would be definitely be a starter ahead of Lingard, Dele Alli or whoever plays in the hole for England. Yes, he may not score many goals (although Benzema rarely stays into the box to get into goalscoring positions). But like I said before, goals aren't everything or else many other great players would be crap if they're judged by goals alone.
Benzema is heavy contributor in other aspects of game and at the end of the day, Real Madrid have been incredibly successful for the past seasons where Benzema has been a key player in their success.
Those 90% of people you're talking about must be football-illiterate if they don't understand Benzema's importance for RM despite being a starter for years by Mourinho, Ancelotti, Benitez and now Zidane.