X11, Flash, and Java were all potential attack vectors whose security is provided for by a third party -- I can see why Apple would want to discourage this.
I wouldn't be surprised to hear that Apple's Radar bug tracker had a few dozen bugs in Safari RSS, maybe even a potential DOS threat, and they chose to move on rather than allocating more resources to an unpopular feature.
More generally, saving space, allowing you to add different things inside a laptop. I realise you could argue the same for hard disk space, but it's not anywhere near as limited.
I had one of the first machine where they dropped the floppy. There were 2 or 3 times that it was a real pain, and the rest of the time, it just didn't matter.
Eventually, I went back to a machine with a floppy, but I wound up using zip drives instead, since the floppies were so damn small (capacity).
(BTW, that's the Powerbook 100 and 5300 I'm referring to above, but I did have a duo 230 and 2300 around that time too.)
I wouldn't be surprised to hear that Apple's Radar bug tracker had a few dozen bugs in Safari RSS, maybe even a potential DOS threat, and they chose to move on rather than allocating more resources to an unpopular feature.