Exactly what I came in here to say. If I said I got free housing, you'd be quite disappointed to learn that by "free" I meant that I owned a home and hence don't pay rent.
Well, IIRC they were buying up 'dark fibre' before the YouTube purchase. So they had already bought the house before they were using it. And in the meantime analysts are trying to say how much rent they are paying... but they aren't paying rent because they bought a house years ago, and now they are making full use of it.
> Its costs for bandwidth are then amortized across the life of its fiber and routers.
It's basically the difference between 'renting' and 'buying', the costs can be (and probably are) significant though.
If you rent some resource you'll be paying bit-by-bit (pun intended), if you own it outright you pay it all in one big 'bite' .
So, their bandwidth bill is far from 0, it's just under a different heading on the balance sheet.