Why do people want to change the composition of the Supreme Court?

It was a campaign issue last time. The claim is that the court is partisan and hopelessly divided. But since 2000 a unanimous decision has been reached about 36 percent of the time. 7-to-2 or 8-to-1 votes happened about 15 percent of the time. People seem to get upset by the 5-to-4 decisions. That happens about 19 percent.
The SC has had several unanimous decisions recently with the Trump appointees. And the latest ACA challenge went down 8–2. What’s the problem?