I suspect that though the author describes running a USB cable to the house, he may be preparing it for remote operation.
(If you can count on it being next to a house where you can run a USB cable, you could also just power it off USB and skip the battery, right? So the battery must be designed in for a reason.)
The mic is a condenser mic, so a pre-amp is needed, XLR or not.
Cheap mics tend to be single-ended things without the balancing transformer or amplifier, so that would all be extra cost. XLR connectors and cables are more expensive. You'd want to go into some audio interface with XLR jacks which is also more expensive.
'remote' also means you can set up networks of them to cover your area. Just dump a bucket every n meters, and spend a few hours driving around every few weeks to harvest the data & swap out batteries.
(If you can count on it being next to a house where you can run a USB cable, you could also just power it off USB and skip the battery, right? So the battery must be designed in for a reason.)
The mic is a condenser mic, so a pre-amp is needed, XLR or not.
Cheap mics tend to be single-ended things without the balancing transformer or amplifier, so that would all be extra cost. XLR connectors and cables are more expensive. You'd want to go into some audio interface with XLR jacks which is also more expensive.