In many universities, major programs for CPSC, physics, etc. require courses with prerequisite chains that take several years to go through. It would be quite hard to build up to these while only taking a minor in these subjects. There are courses for non-majors, but these are typically dumbed down to be made more accessible and possible to jump into without much in the way of prerequisites. For example, there is typically a vast difference between a quantum computing course for physics majors (with a few quantum physics courses as prereqs) and a quantum computing course for non-physics majors.

Meanwhile, talking to the prof and being willing to work a little bit can get you into graduate level history courses even if History is not your major and you've taken next to no History courses. An interest in the subject, time to read, and writing skills honed by other subjects are all you really need. For this reason, I'd argue that History is a great minor to take with a science major, but perhaps not the other way around if you plan to work in a technical field. It's definitely possible for a science major to dive into a senior level undergraduate or graduate history course intended for history majors. Arguably, this is more rewarding that taking a course intended to be an easy option for non-majors.