The CS folks are the architects, engineers, and scientists.
The theories don't live forever, either. With every upgrade in hardware - size and speed of any storage device; networking capabilities; etc.- the CS theories need an update. And those upgrades come fast - every 3-5 years there is a major upgrade somewhere.
The CS folks can only do as well as their specifications allow. And even companies who do their own development in-house won't give the CS folks free rein. Some of those do, however, teach some of the CS folks about the business so that they become part of the specification development process. That's not typical, but it does help to get better results.
No theory lives forever, but some live for a helluva long time. Trust me, for example, the results of the Halting Problem will be relevant for a very, very long time.