It's interesting to think how English youth teams are doing well, but the national side is so bereft of any sort of talent or even depth, especially when you compare England's squad depth with that of Germany, France, or Spain, who could literally field about 4-5 teams that would be at roughly the same level or better than the England team.
It's probably been said to death, but what it comes down to is how few opportunities there are for English players in their own top domestic league, compared to French players in Ligue 1, Germans in the Bundesliga, and Spaniards in La Liga. Lack of modern quality coaching is probably a huge factor as well.