Why didn't the Expander Cycle exist?

They're pretty busy with everything else. I'd rather have gyros and multi-directional RCS before expander cycle. The ability to create unmanned satellites without tinker panel is more important to me than yet another engine type. But I definitely want expander cycle too

I would like the expander cycle as well, when i asked andrew he said they might add it later, dual expander cycle combustion tap off aswell as others. When modding support is added theur will probably be powercycle mods aswell as fuel type mods

The devs hadn’t bothered to add them yet. And we have many other cycles missing too.