If this were true, SCOTUS would almost always be split 5-4. But, it is not. In fact, it typically has significantly more 9-0 decisions than 5-4.
For example: https://www.politifact.com/factchecks/2021/jun/23/trey-wingo...
For example: https://www.politifact.com/factchecks/2021/jun/23/trey-wingo...
That'd only be the case if there were no policies with bi-partisan support. How many of those 9-0 are for politically contentious issues?