The "tech industry" is incredibly diverse to make such a broad generalization. I know for a fact that many players in, say, the telecommunications, chip design and semiconductor industries regularly read their competitors' patents. This helps them not only keep pace with the state of the art, it also helps gather competitive intelligence and guess at their competitors' future directions.

In software, sure, few people read patents. Primarily I'd say it's because a) 99.9% of software development is producing infinite variations of simple CRUD apps, not solving hard problems that require looking up any sort of references, and b) NIH is a like a congenital defect in developers.