JWP seems to be the current focus of the ever-present clamour for someone different to be in the England squad. I really don't think it should be that surprising that isn't in though. There was a period where he was regularly making the squads as one of the backup midfielders, but he never really got further than that, and now other midfielders like Gallagher and Bellingham have come onto the scene and overtaken him.
The Athletic did an
in-depth article about him today. Essentially their point, demonstrated by various stats, is that his assist figures are good but it's all from set pieces and he's not that great in open play.
It's easy to say England should include him for his set pieces, but he wouldn't be getting on the pitch enough to take any, and people like Maddison and Trippier are also set piece specialists but also offer enough in open play to be on the pitch in the first place and finally, England aren't West Ham, our game wont revolve around set pieces like theirs does so he probably wouldn't have the same success from them as he does at West Ham anyway.
Reality is, whoever Southgate picks there will always be someone who people think should definitely be included but isn't. This has been the case for years and years.