Many factors affect bitcoin value.
i) The Internation economic & political condition. If both show stability its value will rise.
ii) The legal development process of Bitcoin also affects bitcoin its value as the Russian Govt legalizes it. Then there was development in its value.
iii)Some epidemic diseases like Covid-19 also fell an effect on its value.
iv)The purchasing or sale on large scale also rises or falls its value.
v) Some good or bad news also fell effect on its value.
There may be some other causes like Gold price or stock market collapse etc.
There is no exact price benchmark for bitcoin, the law of the market is stock and demand that shape the price, currently the community and active bitcoin users continue to increase while the stock is very limited so that the price skyrockets, maybe one day bitcoin will be valued with a definite value such as gold or stocks.