The decision itself is not a huge surprise. I went to every Cardiff GP from 2001 to this year's, and 2024 did have the feel of a final visit.
However, the way it's been handled stinks. If they had doubts about viability, then drop Cardiff when they set the calendar. To put it in, allow fans to arrange (expensive) accommodation etc, then move the goalposts three months later is a huge own goal.