I have developed another theory, for anyone who frequently checks this website for some reason. My new and revised theory is that the Wormhole, the mysterious vortex that nobody has dared to explore yet, is the creator of the tunnels. Or more specifically, some alternate power hungry society/Government lives on the other side of the Wormhole. This alternate society used this wormhole technology that they didn't have before to venture out into the far reaches of the Galaxy. The tunnels would be the result of these alternate universe aliens branching out into the universe, looking/waiting for the Planet. I would like to add that the Angel character may be one of these alternate universe aliens, masking trying to find the Planet as trying to get home. I apologize if this seems far fetched; I just like this game quite a lot.
My Theory (Pardon my grammar): The tunnels were created by the "Government", in a similar way to how the gentleman made his: using the rings and tiles. The "government" was using them as "bridges" to places they thought the wormhole could be, but they later shut down the tunnels altogether. I think tunnel C might also lead to the wormhole because of the fact that it is parallel to tunnel T, where the wormhole was discovered, and also the unsuspected "call" to the authorities. The reason the tunnels are broken apart instead of being a fully enclosed tunnel is because there was a limited amount of tiles the "government" could use.
In the cutscene "Conspiracy", the duplicator mentioned that the Angel might be working for the government, which would explain why he wants everyone to go home; he wants them all to leave, protecting the "government's" tunnels.
Am I hot or cold?
The pastafarian should be able to get the planning make perfect achievement on the river part 4. That is because the game says the light bridges are not tunnel powered - they are Flying Spaghetti Monster powered
I mean, I haven't provided enough information for you to guess the answer, but that's surprisingly insightful for the information you do have.