NTSC DVD native max resolution is 720x480 (ignore more depth like overscan) that isn't 16:9. So most 16:9 titles uses non-1:1 PAR to display 16:9 that isn't ideal for quality. Though anyway any DVD quality is now considered poor regardless of aspect ratio.

Why is non-1:1 PAR bad beyond just the raw pixel count?

I think it's obviously bad for Dot-by-Dot displaying especially on LCD, but I remembered that 480p DbD LCD wasn't a thing.

480p LCD's do exist (or did), iirc they were marketed as "Enhanced Definition" as opposed to the later "High Definition" displays. However, they were 4:3.

Remember it's compressed, so a higher pixel resolution at the same bitrate could end up lower quality.

I guess either my DVDs or my player is garbage because even though it's hooked up by HDMI I often find DVDs with 4:3 menus and then double-letterboxed (so, like, framed) video within.