SDET (Software Developer Engineer in Test) as a title/career path seems to have gone mostly out of vogue in the past decade or so unfortunately. Most companies I've worked for seem to hold the philosophy that the engineers developing the features themselves should do the testing. Which is a legitimate viewpoint, but there are of course pros and cons to everything and not every use case is really suited for that.
I think part of the problem for SDET is that pay bands are often different (read: lower) for SDET, and if you are doing SDET you already probably have the skills to be a developer and are going to opt for the higher pay band/career path. A lot of companies seem to hold a weird perspective that SDET is "lesser" or requires less skills than just a typical feature developer.