1. as a software engineer in test (i.e. QE), you will mostly write Matlab code. Even for many developers, some features are written in Matlab, not C/C++. This will limit your skills, as Matlab coding is not a transferrable skill if you go to other companies.
2. as a QE, you will only know how features work, once you find a bug, transfer to developers to fix. This will limit your skills as well.
3. overall, if you are passionate with coding and development, QE is not a good fit for you
4. salary is not competitive compared to other software companies. The salary is difficult to retain top performers or hire good candidates