In reply to Taurig:
It depends what soft shells you've looking at, I guess...
Then there's the issue of the supposed origin of soft shell; ice climbing, and mostly US, who tend to go for shorter jackets anyway. Ice climbing will assume a harness, so that might influence length.
But you're right that there's no good reason why the designs shouldn't have evolved to a more useful length by now, with the wider adoption of soft shell.
I have an old Montane Soft Tech soft shell in IBQ Thermaskin fabric, and that's a good length. Shame the fabric wasn't quite weather-resistant enough...
Then there's the Patagonia MixMaster, which is a decent length. Also obsolete, of course...
There are a lot of low-end jackets around, from the likes of Regatta and Trespass, and they have terrible armscye designs, almost as if they're designed with classic tailor's block-cutting rules, rather than an active cut. The arm raise is terrible. These might be okay for around town or skiing, but they're hopeless for anything a bit more active, especially climbing.
This active fit is what you pay for in specialist clothing; designers who understand the needs of active users.