Why is 1 Sec HGT not the default DEM for Terrain Correction?

I processed a number of products using default parameters (SRTM 3 Sec DEM) and after importing into QGIS the offset is huge. I reprocessed using SRTM 1 Sec HGT and the overlap looks almost spot on. Why isn’t SRTM 1 Sec the default option?

I think for some reason SRTM 3sec has problem at the moment,

But what kind of products did you process?

I’m processing GRD’s located in Iraq from 2015.

For terrain correction, SRTM 1Sec is surely more helpful and according to my experience, the tiles are downloaded much faster.
In your case SRTM 3Sec might not have been downloaded at all (as mentioned by @falahfakhri, there are connection problems lately) and a flat surface was assumed instead.

I think this is a good suggestion.