Sony uses a mirrorless specific format with the lens mount closer to the focal plane than would be possible with a DSLR. This has some nice benefits for the optical design; you're removing a constraint that happens to be particularly painful for image quality.

For many decades this was the big advantage of rangefinders such as the Leica M.

For Canon or Nikon to do the same it would mean re-releasing their entire line (or duplicating it). Canon kind of doing this with their EOS-M series but they only have a few low-end lenses available. Lenses product cycles are measured in decades, so this is a massive undertaking.

Sony was never successful in the DSLR business and they have a much smaller library of lenses so it makes sense that they are abandoning it completely.

Or keep the viewfinder and have a strictly superior product.