The exam board doesn't just pluck a number out of thin air and run with it. Obviously the amount of time given is proportional to how much time the paper should take, which has been fairly and logically analysed (with extra time given to those legitimately judged to need it, which is not very many at all as a percentage of your year group). If you run out of time then it's down to your poor exam technique, which guess what, you've had two academic years to practise and perfect.
Your teachers have been banging on at you for two years about how much time to spend on each section, how much you should aim to write for each section, how to be concise when you need to, how to write in detail when you need to, etc. They sit there with you time and time again with timed and untimed papers in lessons and revision sessions, going through mistakes you could make and how to correct them. They show you the specification, past mark schemes and sample answers. They tell you to revise the content and practise your exam technique against all of this. Then you still run out of time because clearly, you haven't been paying any attention at all to the people who were trying to help you.