I also think that the only incentive is to make entries about older ones, since the people who update their list every time they watch an episode is a niche group. Lol, I made a list when I watched like 6 anime.
Yeah, that's why I mentioned recency bias. Tastes are subjective, yes, but sometimes I just don't get it when anime get scores close to 8.5. There's this Winter 2018 anime called Yuru Camp, that currently has a great score, and I watched the first two episodes in Jan, and it was the most boring, uninspired bland, thing I watched in quite some time, and I never imagined it would often be compared to a master-work like Sora Yori. But, what I learnt was that for people who liked it, it was 'comfy'.
Old anime have it pretty rough. I've watched very, very few anime pre-2000, and Cardcaptor Sakura was my favourite but its score, IMO, is pretty low(it has like an 8.2, but still). And, the funny thing is the animation holds up incredibly well. Though, the ones around 2006-2010 have the highest scores, since that's around the time the site was in its early years.