In addition to what @ABraun says, you can make DEMs with Sentinel-1, but the satellite is clearly not designed for that. The revisit time is too large and the orbital tube is too narrow. You clearly see that DInSAR-based approaches are privileged (which is a good thing IMHO).
Students in internship in our institution tried their best to make DEMs over several regions but never achieved better results than the free ones.