Jennings average is importantly as an opener and therefore comparing to Bairstow isn't like with like anyway even if both had good tours.
Jennings is possibly seen either as a legitimate option or as cover for Crawley and Sibley with Burns not touring, he's also a superb close in fielder to compliment Pope.
Bairstow doesn't open in test cricket and with Foakes and Morgan isn't needed as a keeper.
Jennings past superb form as a specialist opener against spin on turning wickets makes him and not Bairstow the logical choice.
He isn't an option, he is dreadful
Can't wait till his Lancs contract is up.