I'm not quite sure of the reason. There's a couple of possibilities:
1. DDG is relying on Bing for a lot of their search data, maybe bing's just got better, or DDG have configured their integration better. I don't feel that DDG's had a significant improvement, it definitely feels like they've caught google on the way down more so.
2. Google losing the SEO war. As it gets easier to run and monetise blogspam sites, more of them exist, and as time goes on, a longer tail of topics get "served" by these sites. Unlike the spam of years past which tried to convince Google that their viagra selling site was really about top ten movie downloads, these sites are nominally about the topic the user searched for, so maybe Google is having a harder time trying to evaluate "quality". LLMs are being given a lot of the blame for this, but this is an older phenomenon than that, there were plenty of sites doing e.g. templated articles fed product spec sheet, or pay a minimum wage intern to rephrase the wikipedia page before that.
3. I've cut down my usage of Google services to basically just YouTube and YouTube Music. I also run ublock origin pretty much universally. Maybe my de-Googling has just been successful to the point that Google doesn't have a accurate profile for me anymore, and this has more of an impact on search than I expected.