In my opinion, most of the students would have done great in maths in childhood (say 1st to 4th STD), not because they were studying well, it might be because the concepts were easy.
But what happens after that is slight shift in focus. It's not that they are bad now. It's just that now they start feeling the effect of weak basics.
It all starts with LCM, HCF, Decimals and goes on to find x and y, solving equations.
People who are good with this, can actually focus more on only concepts from here on, whereas the weak student has to focus on both concepts as well as the process to solve.
This gap in understanding continues and student with good basics scores good marks only studying 30minutes a day and a student with weak basics struggles to score average marks even after spending 2-3 hours.
This makes most of the students say, 'I hate Mathematics'