For me, it's that I use a variety of systems and operating systems depending upon the circumstances. Unless it's relatively specialized tools (development environment, heavy-duty photo editing), I'd much rather have a web interface I can get to from anywhere rather than having a native app I can only use on one system. The native app has to be a lot better at some task.
If you run a cron job that turns your feed items into emails[1], you can use your regular IMAP client on any platform. I prefer it over both web clients and native feed readers.
[1] There are a bunch of tools that can do this, but I'm going to give a totally unbiased recommendation for https://github.com/zsau/feedmail/
I don't use a regular IMAP client :-) I read all my email through web interfaces too.
I've been using the free version of NewsBluer and the paid versions of Reeder3 on OSX and iOS for over a year now and I'm really with it (no affiliation with either). For an one-off payment of 18$ (for the Reeder apps) I think its pretty great.
The free NewsBlur does remove unread items older than 7 days or so I believe but the paid version raises that up to a month or so.
Through the combination I get a very good sync of my read, and starred items and Reeder 3 offers some nifty integrations with services like Pinboard and a decent built-in browser and a 'text only' version of the website which makes it easier to read in a small screen.
The code is open source and actively developed, which gives me peace of mind when I pay my yearly subscription.
On my Mac I tried liking Reeder 3, but TBH NewsBlur’s web interface is better. Reeder can use NewsBlur’s API and the syncing between mobile and desktop is nice to have.
NewsBlur’s author has been very responsive to issues and has been actively improving the service.
I also tried self-hosting various web solutions but it’s too much of a hassle, a constant security risk and paying for a VPS ends up being more expensive.