> This is not true. Compile times are usually much better with modules.

What significantly improves compile-times is Pre-Compiled Headers (PCH), which most compilers have supported for decades.

The study you mention, does not show data for them.

Having ported one >1 million LOC C++ app to use modules in two compilers, the compile time improvement of modules over PCH was not distinguishable from noise.

Modules have many advantages, like better encapsulation, etc.

The main thing people want from them seems to be better compile times, which is the one thing they don't deliver, at least over the PCH solutions that have existed for decades, are already supported by all build systems, etc.

Compared to modules, PCHs are "zero-effort" and deliver performance instantaneously.