They synchronize because of thoughts & prayers... Duh! ?

There is a link. Try this Myth Busters vid for grins.

Sheeples.

Because they are coupled, even if weakly, as shown in this demonstration. On the foam board alone, they are decoupled. On the cans they are allowed to oscilate the whole system (even if only a tiny bit) which weakly couples them together and they eventually synchronize. They are then moved from the cans to the counter top (always remainiing on their foam board) and... they eventually go out of sync.

The shifting of the cans cause them to 'fight' each other when out of sync and 'work together' when in sync. That means that when two of them sync up, those two will begin to 'win' the fight with the other three causing them all to fall in line.

Think about having five people on a swing randomly pushing in different directions (while standing ON the swing). If two of the people get together and start pushing in sync, the other three are going to feel it. It will be more work for them to fight the other two (unless they group up, which still works for this argument). Eventually a third gets tired of fighting and joins the first two. Then a fourth and finally the fifth as it's just easier to go with the flow.

This is the same principle but it's more closely tied to conservation of energy. Meaning it takes more work to stay out of sync than it does to be in sync and thus they sync up to conserve energy.

they do it on the same table but if you go too high in number meaning hundreds they don't stay in sink any more

Theyre all a bunch of weak minded followers.

They don't. After seeing the video, I have to say that digital ones that I have used don't.

Mythbusters disproved that.

After thinking about it for ten minutes, I decided the most likely answer is that the individual metronomes somehow become weakly coupled to one another, perhaps through vibration. So I Googled a bit and found this [sciencedemonstrations.fas.harvard.edu]synchronization-metronomes and this [en.wikipedia.org]

[ted.com]

I think the answer is in this.

One hundred metronomes sychronise

Harmonics.

because your brain perciveis a link ,

waiting for a real answer but it must be related to why those suspended clacking balls go from chaos to synchrony