Because you should be able to win half your 50/50 games not none of them.
You've ignored the possibility of a draw. It's 33% chance of winning those games.
The list below is those games against top sides or tough away games. Some of these sides we were NOT even 505-50, such as France in 2017, they were simply a better squad than us
2017:
Germany 1-0 England FRIENDLY
Scotland 2-2 England WC QUAL
France 3-2 England FRIENDLY
W:0 D:1 L:2
2018:
Holland 0-1 England FRIENDLY
England 1-1 Italy FRIENDLY
Belgium 1-0 England WC
Croatia 2-1 England WC
Belgium 2-0 England WC
England 1-2 Spain NL
Croatia 0-0 England NL
Spain 2-3 England NL
England 2-1 Croatia NL
W:3 D:2 L:4
2019:
Holland 2-1 England NL
W:0 D:0 L:1
2020:
England 2-1 Belgium NL
Belgium 2-0 England NL
W:1 D:0 L:1
2021
England 1-0 Croatia EURO
England 0-0 Scotland EURO
England 2-0 EURO
England 1-1 Italy EURO
W:2 D:2 L:0
2022:
Germany 1-1 England NL
England 0-0 Italy NL
Italy 1-0 England NL
England 3-3 Germany NL
W:0 D:3 L:1
2023
England 2-3 France WC
Italy 1-2 England EURO Q
Scotland 1-3 England FRIENDLY
W:2 D:0 L:1
TOTAL:W:8 D:7 L:10
So we are overall slightly below win rate under Southgate IF you think we had a squad just as good as Belgium, Spain and Croatia in 2017, which we didn't. So we probably performed about on course.
The last 3 years is interesting though, our squad is much better than it was 3 years ago, and southgate has set them up to improve their results, we've over performed slightly. TOTAL for last 3 years: W:4 D:5 L:2