The trend isn't honestly that weird or disturbing.
Spec is more fun - there's a larger variety of concepts that are all a bit disconnected from each other. When you study vectors, it doesn't feel like you're doing complex numbers, and when you study mechanics, it doesn't feel like you're doing calculus. But everything still feeds in together - unlike methods, where everything feels like everything else, with the exception of probability which is almost universally despised.
The exams are easier - methods has less difficult content, and so makes up for it with harder separator questions. Spec has more content, and it's harder, so they can get away with less difficult questions.
If you can get above 30 in methods, then you know enough content to do well in specialist. Anything past 35, and you have a good enough brain to do well in specialist. Everything after that is all the types of questions and luck on the day.
That's the other thing a lot of people don't realise (which was mentioned above) - a lot of it is luck. The difference between a 40 and 50 sounds as big as the difference between 30 and 40 - but between 40 and 50 is only 8%. People here are separated by, sometimes, fractions of a percent. It doesn't matter how well you prepare, you only have an hour or two to do these exams - if in one of them you miss the fact that they wanted a specific form, or did 2+2=2 without thinking, it's really easy for that one mistake to cost you a study score. In methods, it's easier to make these mistakes because there are more fiddly questions - in Specialist, it's not.