It’s not really a bandwagon argument, I’d call it a statement of the de-facto standards regarding attribution of MIT licensed open source software
Or to put it in technical terms, the license says absolutely nothing about attribution, so it’s fine for people using the library to assume that we don’t require it, and it’s also fine for you to add attribution to your projects if you want.
However, the license does say that you have to include a copy of the license if you include a largely unmodified version of three.js in your code:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.