CMake build only subprojects, but not top-level project

Question

There is top-level project named 'cppserial', which depends on subproject 'cppstreams', which also depends on subproject 'cpputils'. The file structure of whole project:

cppserial/
  |
  CMakeLists.txt
  src/
    |
    cppserial/
      source files
  libs/
    |
    cppstreams/
      |
      CMakeLists.txt
      libs/
        |
        cpputils/
          |
          CMakeLists.txt
          src/
            |
            cpputils/
              source files
      src/
        |
        cppstreams/
          source files

cppserial CMakeLists.txt:

cmake_minimum_required(VERSION 3.8)

project(cppserial)

set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

set(SOURCE  ...sources...)

add_library(${PROJECT_NAME} STATIC ${SOURCE})

add_subdirectory(libs/cppstreams)
target_link_libraries(${PROJECT_NAME} PUBLIC cppstreams)

target_include_directories(${PROJECT_NAME} PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/src")

cppstreams CMakeLists.txt

cmake_minimum_required(VERSION 3.8)

project(cppstreams)

set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

set(SOURCES ...sources...)
set(HEADERS ...headers...)

set(BOOST_ROOT D:/Development/CXX/Libraries/Boost)

find_package(Boost REQUIRED)

set(Boost_USE_STATIC_LIBS ON) 
set(Boost_USE_MULTITHREADED ON)  
set(Boost_USE_STATIC_RUNTIME ON)

add_library(${PROJECT_NAME} STATIC ${HEADERS} ${SOURCES})

add_subdirectory(libs/cpputils)
target_link_libraries(${PROJECT_NAME} PUBLIC cpputils)

target_include_directories(${PROJECT_NAME} PUBLIC ${Boost_INCLUDE_DIR})
target_include_directories(${PROJECT_NAME} PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/src")

cpputils CMakeLists.txt

cmake_minimum_required(VERSION 3.8)

project(cpputils)

set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

set(SOURCES ...sources...)
set(HEADERS ...headers...)

add_library(${PROJECT_NAME} STATIC ${HEADERS} ${SOURCES})

target_include_directories(${PROJECT_NAME} PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/src")

Building:

cd build
cmake ..
cmake --build .

Build output:

[main] Configuring folder: cppserial 
[proc] Executing command: D:\Software\CMake\bin\cmake.EXE --no-warn-unused-cli -DCMAKE_EXPORT_COMPILE_COMMANDS:BOOL=TRUE -Sd:/Development/CXX/cppserial -Bd:/Development/CXX/cppserial/build -G "Visual Studio 17 2022"
[cmake] Not searching for unused variables given on the command line.
[cmake] -- Selecting Windows SDK version 10.0.19041.0 to target Windows 10.0.19044.
[cmake] -- The C compiler identification is MSVC 19.33.31630.0
[cmake] -- The CXX compiler identification is MSVC 19.33.31630.0
[cmake] -- Detecting C compiler ABI info
[cmake] -- Detecting C compiler ABI info - done
[cmake] -- Check for working C compiler: D:/Software/Microsoft Visual Studio/2022/Community/VC/Tools/MSVC/14.33.31629/bin/Hostx64/x64/cl.exe - skipped
[cmake] -- Detecting C compile features
[cmake] -- Detecting C compile features - done
[cmake] -- Detecting CXX compiler ABI info
[cmake] -- Detecting CXX compiler ABI info - done
[cmake] -- Check for working CXX compiler: D:/Software/Microsoft Visual Studio/2022/Community/VC/Tools/MSVC/14.33.31629/bin/Hostx64/x64/cl.exe - skipped
[cmake] -- Detecting CXX compile features
[cmake] -- Detecting CXX compile features - done
[cmake] -- Found Boost: D:/Development/CXX/Libraries/Boost/lib/cmake/Boost-1.80.0/BoostConfig.cmake (found version "1.80.0")  
[cmake] -- Configuring done
[cmake] -- Generating done
[cmake] -- Build files have been written to: D:/Development/CXX/cppserial/build
[visual-studio] Patch Windows SDK path from C:\Program Files (x86)\Windows Kits\10\bin\x64 to C:\Program Files (x86)\Windows Kits\10\bin\10.0.19041.0\x64 for D:\Software\Microsoft Visual Studio\2022\Community\VC\Auxiliary\Build\vcvarsall.bat

Compiling output:

MSBuild version 17.3.1+2badb37d1 for .NET Framework
  Checking Build System
  Building Custom Rule D:/Development/CXX/cppserial/libs/cppstreams/libs/cpputils/CMakeLists.txt
  ...source files...
  cpputils.vcxproj -> D:\Development\CXX\cppserial\build\libs\cppstreams\libs\cpputils\Debug\cpputils.lib
  Building Custom Rule D:/Development/CXX/cppserial/libs/cppstreams/CMakeLists.txt
  ...source files...
  cppstreams.vcxproj -> D:\Development\CXX\cppserial\build\libs\cppstreams\Debug\cppstreams.lib
  Building Custom Rule D:/Development/CXX/cppserial/CMakeLists.txt
  Building Custom Rule D:/Development/CXX/cppserial/CMakeLists.txt

As you can see, only subprojects are being built. There is no cppserial.lib in the build folder. I can't understand what could i miss.