Its Switzerland, so I'd assume the mountains and snow play a big part in increasing the cost of surface road building and snow clearing, making tunnels more attractive.
Most of the area of the map does not get intense snow.
It is in the northern part of Switzerland, the very lowlands of the alps. In my two winters here there would be a few weeks of mild snow, at the very most in this area (and the first winter here had a 1 in 10 year blizzard).
And there are some topographical changes, but nothing very steep. There are 100 KPH highways all throughout this area, and more convincingly, fairly high-speed rail too.
The problem is more that the Swiss Plateau (where most of these tunnels would be built) is very densely populated. There's just not enough room for a whole new road network to be built on the surface.
Yeah, I think this might have been one of the reasons why no one created an initiative to stop this. If instead they proposed a surface railway a few communities might have objected.
Since this is in Switzerland, an overland route will require a lot of ups/downs over all their mountainous terrain. A tunnel can be made to slope much more gradually, which will increase the efficiency of the system. In addition, Switzerland has a lot of experience with building tunnels, so it's probably not quite as costly as it could be.
Private land ownership - since we don't talk about China but very strong democracy, state can't really just come and take piece of land (often cut through fields), and have terminals cut through already densely populated cities.
1 farmer not agreeing in some crucial placement would cancel whole part of network. And buying up so much land could easily be more costly here rather than just digging up rather simple narrow long tube.
There isn't that much free land for new tracks, plus mountains everywhere. If any country anywhere called for an underground network, it would be Switzerland.
Underground is really, really expensive, for urban areas, I get it, but I wonder why it couldn't 'mostly' be above ground, like rail infrastructure?
Underground passes for bypassing major roads, but otherwise, above ground where possible?
Apparently, 'near surface underground' which can be achieved via scraping is much less costly than tunnel digging?