Sometimes that's effort that's not really necessary. At work we had a team build a dashboard with React and a few graphs recently. It clocks at 2000 unique dependencies. That's not a typo, it's two thousands dependencies for a few graphs. Reimplementing all of that would take many man-years of work, but I think it wouldn't be necessary in the first place. Chart.js doesn't use any runtime dependencies, and could probably fill most of our needs. Chart.js is 50k of Javascript, which is a lot but probably more than we need. I don't know how much time it would take to make a reimplementation to have the API we need, but I think it's doable. Why would we want to do that? Because those 2000 dependencies are a liability. Last time I checked 165 were looking for funding. It would be easy to imagine a malicious actor paying a few people to contribute to low profile but widely used JS libraries, and take over the maintenance when the original maintainer becomes tired. I don't know if this is a worse liability than developing our own chart library. I don't know much about security and the tradeoff involved.
All of that to say, isolation from the broader ecosystem may be a good thing.