Why ACTS texture format is not available in runtime?

As I understand, ACTS is a special kind of compression, that could be used by GPU. In my application I can observe, that ACTS textures takes much less memory, then textures I load from PNG files. And I wonder to compress these loaded textures with ACTS also. But looks like it is not possible in the runtime.
Do I understand ACTS correctly?
Why compression is not possible during runtime? Do it have some special hardware restrictions? Which restrictions? Why I never met these restrictions during build on different devices?