Interesting video some will understand and some will mock. "Those who have ears to hear, will hear"
The answer, of course, is as follows:
God DID show Himself, multiple times. Each time, how long did it take for man to not only doubt He did, but to insist He never did? A few generations at best. Let's look at what would happen if God were to, say, show up at the halftime in the Superbowl.
1. A lot of viewers, and even those in attendance, would immediately marvel at the "special effects", not believing that it was really happening. I mean, we had idiots claiming the planes hitting the WTC were just holographic projections.
2. The talking heads on TV would spend hours trying to convince people that it didn't really happen, that it was an atmospheric phenomenon, mass psychosis, etc. Video evidence would mysteriously be "lost".
3. Within a few days, random internet keyboard jockeys would be playing heavily edited video clips purporting to show how it was faked, etc.
4. Within a few years, the conventional wisdom would be that something might have happened, but we don't know what it was so we're going to ignore it. Those who believed it would be mocked and marginalized.
For examples of what I'm talking about, look at two recent events, the Holocaust and the moon landing. They are among the best documented events of the modern era, extensively researched, with millions of witnesses who spoke out about what happened, and in the case of the moon landing, thousands who worked on the project. We have museums dedicated to preserving the history of what happened. Yet, what do we see? Increasing numbers of those eager to downplay and ultimately claim they didn't happen. In another hundred years or so there will be official debates about whether the Holocaust actually happened, and many will be claiming the Jews should just forget about it because they're using fairy tales to justify their vigilance to avoid a repeat.