OBoile

For most of us, nothing prevents it, or using an e-bike or any of the other things listed.

The thing is, doing a virtual "race" costs me nothing other than making sure I'm riding at the start time. So it's pretty easy to do it for fun and not take it so seriously. I see it as a, relatively speaking, fun way to get in a ~1 hour hard ride. If someone else is cheating, I'll never know, and frankly, I don't really care. It doesn't detract from the experience unless you let it.

For the actual serious races, I think they generally have most of the top riders ride at a specific location where they can be weight. But even still, there have definitely been examples of cheating. IIRC one world tour rider listed his weight at 10 kg lower than it actually was.