Why it the default platform ubuntu 16.04 which is obsolete

AI moves fast, I wonder why TFRT is still developing with Ubuntu 16.04 while nearly everyone these  days are using newer Linux platforms(e.g. ubuntu 20.04)?

Even the major build tool bazel is not up to date(ubuntu 16.04|18.04 only) https://docs.bazel.build/versions/3.7.0/install-ubuntu.html

Is this just document out-of-date or I actually need spin a virtual machine for 16.04 to build TFRT?
