I’ve been down this road, re-encoding is always lossy, you’ll end up with smaller files with no “noticeable” compression artifacts, but the original MPEG2 will still be of superior quality.
This is true and is probably why IA doesn't re-encode them. However, if you just want your own personal copy to re-watch them I don't think this is really that big of a problem. Ideally IA would keep the originals for archival purposes and make re-encoded versions available as well, but I expect they don't because they have limited resources.