Improper default value of installation prefix on Linux

When I install Qt Creator from sources, by default it tries to write its files to /lib , /bin, /share directories, which is incorrect. Usual behaviour expected from Unix program is to choose /usr/local by default, i.e. install files to /usr/local/bin/ /usr/local/share, /usr/local/lib. Invocation of

make install INSTALL_ROOT=/usr/local

fixes the problem, but this solution is not obvious and not documented anywhere