Because the competitive landscape of the web is such that the site which looks and works best gets the most traffic, developers and designers put a premium on the presentation of that content and let structural markup take a back seat. ↗
There's this very vulnerable planet of ours with finite resources. Architects and designers have, I think, a fair responsibility for conserving energy and materials, and making things durable. ↗
But, having a perfume and license, in general, is a financial necessity. A designer must, to reap back the money spent on prototypes and all that sort of thing. ↗