Because a hypothesis is "an educated guess" which was only a proposal. The purpose of an experiment is not to support the hypothesis. It is to validate the hypothesis and see if it was correct or not. If the data does not support the hypothesis, it must be changed, or rejected in favor of a better one.
In many cases, researchers may find that the results of an experiment do not support the original hypothesis. When writing up these results, the researchers might suggest other options that should be explored in future studies.
There are many ways to come up with a hypothesis. In many cases, researchers might draw a hypothesis from a specific theory or build on previous research.
When trying to come up with a good hypothesis for your own research or experiments, ask yourself the following questions:
Is your hypothesis based on your research of a topic?
Can your hypothesis be tested?
Does your hypothesis include independent and dependent variables?
Before you come up with a specific hypothesis, spend some time doing background research on your topic. Once you have completed a literature review, start thinking of potential questions you still have.
Learn more about creating a hypothesis at VeryWell.com.