This is always true. There are only some specific device classes which can be used as Alexa routine triggers at the current time. You got started in the right direction, you just need to use a different kind of virtual device.
Please see the community FAQ on this use case, it will show you what you need to do.
Note that the instructions are different if you do have a SmartThings/Aeotec hub or if you don’t, but the basic idea is the same.