If RSS really were popular, you would expect Google closing Reader to spur Mozilla and Apple to put even more work in maintaining their RSS readers, to attract people to them.
However, RSS was never very popular outside some small tech circles, and Mozilla and Apple saw that the same way that Google did.
That assumes that Mozilla and Apple were capable of doing those things in that time period.
Mozilla is nothing more than controlled opposition that Google can prop up and say "See, we're not a totally monopoly" while Apple at the time could see nothing beyond the piles of money that the iPhone was making them, to the point where even their desktop/laptop lines suffered.
However, RSS was never very popular outside some small tech circles, and Mozilla and Apple saw that the same way that Google did.