The old trap of tech debt. Basically... back when these tooling projects started, stuff like casting stuff around all the time, using un-optimized tree algorithms, inefficient value objects or whatever didn't matter - because the projects that were built using them were so small the inefficiencies didn't matter. And once the projects got bigger, inefficiencies weren't really looked at for three reasons: the obvious "if the source gets larger, the build time goes up as well", because people simply got more powerful hardware - and finally:
Because most JS developers simply aren't your old guard neckbeard coders with decades of experience under their belt. They're fresh coding academy graduates that don't teach stuff like flame graphs or performance tracing in general, and simply are used to stuff taking a lot of time. And fwiw, knowledge of optimization techniques isn't really widespread even in senior developers. Modern computers are simply "fast enough" for many people (and especially corporate beancounters) to not care.
Your customers don't run SVGO and only care about the performance of the output. Devs care, but not enough to do anything about it. Companies care about dev productivity, but the cost of the hours to run through the profiler isn't something they are willing to pay for.
And finally, there aren't enough maintainers/contributors to these projects. The core team is some volunteers. When they have spare time for the project, it's almost always going to be used to keep up with web standards, add missing features, or chase down bugs that impact the final output. They know performance matters, but thers's always something more important to do instead.
Because most JS developers simply aren't your old guard neckbeard coders with decades of experience under their belt. They're fresh coding academy graduates that don't teach stuff like flame graphs or performance tracing in general, and simply are used to stuff taking a lot of time. And fwiw, knowledge of optimization techniques isn't really widespread even in senior developers. Modern computers are simply "fast enough" for many people (and especially corporate beancounters) to not care.