It is widely used by companies that receive a very large number of applications, like the FAANGs and the ones @ucla_cs_god mentioned (some firms use HackerRank instead, and many Wall Street firms prefer HireVue).
However, I still doubt that 75% of all CS students take this test, because many students (from the less competitive colleges) simply apply to local opportunities, and most of these firms don’t need CodeSignal.