Because they are currently better for most multi-core graphics applications.
It wasn’t always like that. Intel ruled the roost and although AMD processors delivered more bang for buck, the I7’s would always beat them on performance. This is how it was for years and years. I recently upgraded to a Ryzen 7 CPU. Before that, I had an i7 and I didn’t need to upgrade my CPU for 8 years. It handled anything I threw at it. But when I did upgrade, things had changed around.
Recently, AMD have pulled ahead with the Ryzen line of processors, but Intel keeps fighting back. You have to keep your ear to the ground. Keep checking out benchmarks when new processor lines land.
For now, generally, ryzen’s outperform their equivilent Intel processors. That may change soon. We don’t know.