Why do big companies ask for conference instead of journal publications? It is generalized that journal publications are normally more complete research papers than those in conference proceedings. However, when applying for a job in the industry, most companies (e.g. Facebook) ask for first-authored publications at peer-reviewed conferences (e.g. ICRA, RSS, IROS, or similar).
Why is this? Are these top conferences more valuable than top journals like Nature or Science from an industrial standpoint? Why could this be?
It depends on what field you are in and the types of jobs you are looking at. In computer science, conferences are typically valued more than journals, although this doesn't necessarily mean the quality of the papers at conferences are better than journals. A popular computer science department ranking site, CSRankings, does their rankings by top conferences, where the three you list are used in the Robotics area.