Human history is short because people only invented writing a very short time ago. We typically say that history can only exist when there is writing so that events can be recorded.
Human beings have only been able to grow food for themselves (as opposed to hunting and gathering) for something like 10,000 years. Before that, writing was not at all likely to develop because there was no need for it. With agriculture came governments and business and other things that needed records kept. This led to the development of writing, which is believed to have started around 6000 BC. The Sumerians developed the first known system of writing by 3400 BC.
Writing is not an obvious thing for people to do. It therefore took a long time before writing was invented and history could begin.