Escape pods are lifeboats. They're for keeping people alive until a rescue ship comes to pick them up, and maybe landing on a planet they're already orbiting. They have only the tiniest of maneuvering thrusters, which are in no way able to traverse astronomically significant distances. Again, Janeway's instruction to seek out new life and new allies would be like the captain of the Titanic telling passengers to go out and swim for help - except in this example, the Titanic, while badly damaged for sure, was not actually sinking, just adrift.
Straight up? The writers wanted to heighten the drama by removing the comfort of seeing crew extras from the shots, so they went with an incredibly and obviously idiotic explanation for why said extras suddenly were no longer around. And it worked, in the sense that the extras stopped showing up, for reasons explained in the dialogue.
But said reasons remained incredibly and obviously idiotic.