Subspace Conduits have not been explained in great detail but it has been suggested that they may be natural Quantum Slipstreams but we don't know this for sure. (Natural transwarp conduits seems more logical to me, but it seems Voyager has decided that transwarp conduits are naturally occuring. See transwarp for more details.)
We do know that they're naturally occurring (not the best word. They don't come and go as far as we know. the known network in the Delta Quadrant has been around for thousands of years or longer.)
Apparently they do "wear out" or something as the Vaadwaur claimed that they had to be "maintained".
They were controlled by the Vaadwaur thousands of years ago but they were almost entirely wiped out by enemy races and the conduits are now "controlled" by the Turei, among other.
Source: Star Trek Voyager episode Dragon's Teeth (VOY)