Although I am a long-time consumer of GIS SE content, I am still a relatively recent contributor of content (approaching 4 years). In the four years since I started contributing, especially the last couple, it kept feeling like engagement on GIS SE was dropping. I decided to look at Stack Exchange Data Explorer to see if the data backed up my impressions.
Looking first at Questions, Answers, and Accepted Answers By Year (PostsWithDeleted):

And then looking at monthly totals for the past 5 years:

The number of questions peaked and started to decline in 2016, but the questions really began to drop off around 2023. I know AI chatbots are obviously a factor, but questions were already accelerating their decline before 2022/2023.
This gets me back to the title of this question, how does a community maintain value when the level of engagement continues to decline so rapidly? What things are being pursued to improve engagement?