Network investments actually increased in scalable infrastructure and support capital expenditures. Stand alone "broadband" costs have decreased mainly because the equipment involved no longer just provides internet connections.
So instead of looking at just "upgrade/rebuild" spending (which TWC did massively over the last 2-3 years converting most systems to 860 and 1 ghz) and only "broadband" costs, looks at the bigger picture. Much of the equipment is getting "blended" as time goes on. Equipment such as CMTSs which previously were only used for internet connections are now also used to provide phone service and increasingly 2-way connections for cable boxes.
Replacing a DOCSIS 1 or 2 CMTS with a DOCSIS 3 CMTS is not a "upgrade/rebuild", it's "scalable infrastructure".