Sorry for the looonnnng delay in response. I didn't realize there was a question for me.
You ever try digging a post hole, installing and stabilizing the post, then removing the post, and later doing it all over again in the same place? Without special equipment, the hole is way too wide to keep the post vertical unless you backfill all around it. Then, once you've backfilled the hole, you have to pack all that backfill soil down to keep it straight and steady. Assuming they did this, they then, allegedly, UNpacked the hole, lifted the near-500 lbs. up and out of it, removed the body from the cross/stake to bury him, and did what with the pole? Brought it back to town for the next victim, apparently.
It isn't that the Romans couldn't have done this at all, it is that they couldn't be so stupid to try doing it over and over when it is SO MUCH more practical to just LEAVE the upright pole(s) in place. Doing this setup and removal time after time for victim after victim would quickly render the entire surface of the top of the hill very difficult to perform executions on. The hole would get wider every time. Soil would get packed down in many places and eroded/broken off in others. You'd have soldiers complaining about putting those freaking poles up and down all the time. Engineers would be fired for designing such a dumb system of execution when leaving the upright poles in place is something a little kid could think of.
The Romans were pretty advanced for their day. I can't believe they'd have had the execution system as it is popularly portrayed.
Once you get a post in the ground and solid, you leave it there.