It takes effort proportional to the number of content creation methods, though, not proportional to the amount of content. On an amortized basis the effort is tiny, and the gain is often greater than the cost. Even if you want to argue the gain is tiny itself.
And, frankly, that's already a dubious claim and getting more dubious. An RSS subscriber is very "stickied", and thus very valuable in a lot of ways. I mean that even beyond mere money. A lot of the other putatively "better" approaches are a great deal less powerful, again, because you don't own it, the "better" service does. Witness the way Facebook decides whether or not your "subscribers" get to see your posts, making them a great deal less valuable than an RSS-subscribed reader. I expect this to play out over and over, and for RSS to retain its position of indicating "I am a serious subscriber" for a good long time.
Facebook et al can offer you a better short-term outcome, but as such things scale up, the incentives pretty inevitably turn towards trying to capture the value of your subscriber base themselves. RSS disintermediates that fairly successfully. And since nothing particularly stops you from offering that on the side... why not?
Case in point, a client of mine (one of the top 2 or 3 US corporations you might think of off the top of your head outside of tech) wanted to start publishing a daily email digest of content aggregated from all their content outlets. I tell them OK, send me all your feeds, I'll whip it up in no time, and there it was, delivered early and under budget. They publish on Wordpress, Tumblr, etc, sites that give you RSS feeds without work.
It's much easier to go to /rss and get the content than have to coordinate with however many teams and organizations it took to create all those sites.
Which ones have you tried? For me, RSS readers are a pretty personal thing, like text editors. People have preferences for how they want to read this stuff.
I haven't used one since Newshutch shut down back in 2009 or so. I can't remember the names of any that I tried except Google Reader, which I used for about... 20 minutes total?
Probably not coincidentally, that's about when I started using HN.
InoReader(.com) is the only one I've found post-Google Reader that gets out of my way and lets me read things. The experience on mobile could be improved, but it works well enough for me.
But publishing it takes effort, and if usage isn't high enough people might stop.