Maybe people have successfully made time machines but didnt realize that our galaxy cluster is traveling like 350 miles a second. And so they traveled back or forward in time and end up in empty space and thus die and cannot reveal to us that their machine worked.

I guess a true time machine would need to be able to move temporally and spatially. Also, anyone know how fast earth is travelling compared to background radiation/total stillness in reference to the universe? Oh shit, what if the universe is traveling too. Is an absolute stillness even possible for reference?