It's on its own axis because the blue line represents the number of open tech jobs across all disciplines, whereas the red line is engineers only.
That is, it's more important to know whether we went from 100K to 110K (and how 110K job-seekers compares to the number of job openings) than from "0" to "10".
Side note: how can the "Q4 so far" graph only go up to ~1-2000? More people than that were laid off from Twitter alone.