Well, for one thing, every instance of mission critical hardware needs a full test, because hardware is messy and stuff happens. You wouldn't want someone hurt because a gate on a chip got a stuck-at fault or one of your vendors had a little extra variation etc etc.

Software only needs testing when the tools or inputs change. So design for testability of software is driven by the needs of a development group (eg simulators, debug statements), while hardware (at a minimum) is aimed at a post production group (eg JTAG, test fixtures).

I agree there are many parallels, but I think the culture is different.