Perhaps it's not, but my gut feel is that those other systems mitigate failure by using a smaller number of large, reliable and expensive carriages. Whereas this system is going for a large number of smaller, cheaper(?) skates. It just feels like it's more susceptible to failure?

As someone who gets the train a lot (Brit) - the big expensive ones have to stop due to issues very frequently because of this head-of-line blocking issue. I'd say ~1/4 of the trips I take half a delay of some sort for this reason. (I am trying to make some effort to account for the observation bias of it being f*cking annoying.)

Design the skates so that one can push another at reduced speeds. Bang, built in redundancy.

How will the skates know that the one in front of it has broken down and need to be pushed? Especially when it's operating at 120mph?

Yes, I know that. That now means you need a way for the skates to communicate with each other and maintain a safe distance from each other before they collide and obviously slower speeds. That bare concrete tunnel is now longer bare since you will need communication access points, fibre cables for redundancy, etc.

They're going to be running cables for lights. Its not much of a stretch to put in communication cabling as well.

It makes sense to have the skateboards fully connected as part of their 'autonomy.'

Sensors in the tunnel and the skates, that communicate with each other? It's not rocket science, that's how it's worked for years with trains and subways and even car tunnels have continuous monitoring and signage to alert other drivers.

So you are re-inventing a train?

Just wait for a post talking about how they're replacing the tires with revolutionary metal pathways to save wear.

Because the failure rate per passengers transported is much much lower in a traditional transportation system. All the passengers that they will move per day (and a bit more), with 187 travels, are moved in one minute by just two trains in an underground system. So you have to multiply the risks by the increased travels needed to move the same amount of people. A ratio of ~95 seems quite a lot to me..