Infrastructure has to be robust, and making software robust is currently too boring for many developers.

New product development is driven by VC funding.  VCs have a 5 year time horizon.  There's no funding, thus no time, for the required 'Quality Control testing - Quality Assurance testing - Redesign' iterative cycle to achieve "robustness."

Second, in most companies the product development team and product test team are in different departments with different reporting structures uniting at the uppermost of Upper Management where the final decision is taken by someone knowing bugger-all about product technology and mainly focused on short term profitability.

She believed in nothing; only her skepticism kept her from being an atheist. -- Jean-Paul Sartre