What is the logic behind what sets are available for Limited play?

I loaded up Arena today for the first time since Bloomburrow, looking forward to trying out draft for the latest set (which appears to be Foundations). I open the Events tab and it's not available. In fact, not even the set before that (Duskmourne) is available. It's still only Bloomburrow, and for some reason March of the Machines.

What is the logic behind this? It's not a great new/returning player experience. The choices behind this product continue to baffle me.