It could just be that it requires scale.
Some science projects just can't be done by small research teams.
You mention our understanding of physics. That understanding only got pinned down and refined by spending billions on large research projects.
The only brain related research project I know off that has a budget even close to what we routinely spend on physics is the Human Brain Project [1], and that only started in 2013. It's not expected to be complete until 2023 and even then it is only laying the foundation for more ambitious projects to build on.
You mention our understanding of physics. That understanding only got pinned down and refined by spending billions on large research projects.
The only brain related research project I know off that has a budget even close to what we routinely spend on physics is the Human Brain Project [1], and that only started in 2013. It's not expected to be complete until 2023 and even then it is only laying the foundation for more ambitious projects to build on.
[1] https://www.humanbrainproject.eu/en/