Xen provides a great security design and a protocol to do hypercall that makes sense (unlike kvm+virtio which is DMA all the way, with all the plus in terms of simplicity but the bad on the isolation aspects).
If I wanted to caricature the situation: KVM is more simple to work with in terms of dev (you have results fast), but kind of "fuck security".
Xen is hard from the dev perspective, because it's a more micro kernel by itself, and you can't cheat to have access to the memory, you have to use grant tables (see https://xcp-ng.org/blog/2022/07/27/grant-table-in-xen/ ).
So if a part of the industry took a shortcut, doesn't mean Xen isn't still relevant :)
If I wanted to caricature the situation: KVM is more simple to work with in terms of dev (you have results fast), but kind of "fuck security".
Xen is hard from the dev perspective, because it's a more micro kernel by itself, and you can't cheat to have access to the memory, you have to use grant tables (see https://xcp-ng.org/blog/2022/07/27/grant-table-in-xen/ ).
So if a part of the industry took a shortcut, doesn't mean Xen isn't still relevant :)