Actually not true. Many large projects continue to use SCons and new projects as well.
I don't think in 2018 we had our heads in the sand about SCons' performance.
As project maintainer I've (along with other community members) have been working on performance since at least 2016.
As the maintainer of SCons I can assure you that we are aware of SCons's performance issue.
The page in question is actually quite old at this point.
Since the content was written Ninja, Cmake, Bazel, and other build systems have launched and become mature.
We are slowly working through the easiest of the list of known performance issues.
In addition MongoDB has contributed their Ninja file output logic.
We expect to integrate that in the next major release.
Projects like MongoDB, Godot, VMware, PlatformIO, and many others use SCons.
One of it's strengths is the ability to correctly build complex builds.
Please engage with the community our users mailing list, IRC Channel, or discord server if you're a user.
One frustration for the project is that users run into issues using SCons and never reach out and ask for help.
Many times a small change in usage will resolve whatever has a user stuck.
I'm the current SCons project Co-Manager. Nice to see spirited conversation.
A couple data points on performance. A current snapshot of MongoDB's repo will do a null incremental build in 53 seconds on my i7-2600 with non-ssd drive. (Null incremental build = fully built tree. no need to rebuild anything).
In the last few releases we knocked that down from about 63 seconds.
Currently we're working on a number of performance related items and hope to make some strides here.