Yes, maybe the subject content isn't very difficult. However, i'm going to admit that i find juggling 10 different subject into a week, some of which i don't like, difficult.
I also think that unless you get lucky, getting A*s do actually take a fair amount of effort.
Not everyone is from a privilaged backround, and with little motivation some people do not get any support whilst studying.
Not everyone who gets "bad" marks is stupid anyway, there is also a certain "skill" to knowing what a sometimes very specific markscheme.
To some extent, untill i got a gigantic E for an art sketchbook, i was as ignorant as you.
Also to add to the conversation, i'd say for a standard student who goes to a "good/v.good" school ect maybe something like this:
A*
A*
A
A
A
A
A
B
B
B
Eg a couple of A*, majority As and a couple of Bs perhaps. Most people would think these grades are great i reckon.
However, if someone ends up taking wrong GCSE subjects, potentially 4 grades could be ruined as a result of choices made in y9.