[nickorlow]

I'd think it's because they're introducing updates to address issues w/ the hardware quickly and want a rolling-release distro so users can get the updates faster.

[vitorsr]

Debian testing is about as stable as it gets while also being a rolling distribution. The promotion of package updates from unstable to testing does not take that long either depending on the severity. I would venture a guess that there is more to it.

[mappu]

Testing doesn't get timely security updates. Arch is more like Sid anyway.

[nickorlow]

Community also likely plays a role. Arch users are typically more proactive at fixing things themselves and contributing.