They basically chose the least effective, most expensive option. The option they’ve already proven is a failure on a small scale with convention center.
Speaking of expensive - if they stop the service (or even never start it) - who will maintain the tunnels? Looks like huge liability. Would refilling it with some material actually work (in terms of possible surface buildings damage)?
Which I am sure will be used as a proof that infrastructure investment into anything else but cars is a bad idea, in due time.