Because we live in a geologically stable world where there are no earthquakes or terrorist bombings. There are some long tunnels in China, because spending money on infrastructure directly translates to a higher GDP. Here’s a link to some fun viewing for people who think tunnels built by societies known for graft and corruption are a great idea.
There’s more of the prefabbing of tunnel sections in the Far East (China, Korea, Japan), but Norway has a few of these I think. Could be a good choice for the Straits of Messina, IMHO. Problem there, and in the Greek Aegean (where it would be very handy) is seismic activity. “Better turn on the wipers, AHHHHHH [glug glug]...”