Some software requires 64-bit, like the Atom editor.
I myself am curious as to why something would not work. There must be new features in the 64-bit architecture.
I don't know off-hand any software specifically built for aarch64 that couldn't be compiled for aarch32 as well. I'd be interested in hearing about it though, and what 64-bit provides that 32-bit doesn't, when we're talking about a device with under 4GB of memory anyhow.
I was also under that impression, but then again I'm not really a HW guy. But reading this thread (https://www.raspberrypi.org/forums/viewtopic.php?f=63&t=1382...) shows that I was wrong with thinking that 64Bit was only a RAM benefit.
Somebody tested the RPI against another board that also has the Cortex-A53 processor and saw in some cases some dramatic improvements (3x the performance). Very interesting read.