"could have easily been supported"

While true in the abstract, who will do that support? Python core developers are stretched enough as it is. Why should they volunteer for that?

"not providing any tooling to automatically convert python2 to python3 code"

They did - https://docs.python.org/2/library/2to3.html ("2to3 is a Python program that reads Python 2.x source code and applies a series of fixers to transform it into valid Python 3.x code"). In practice that turned out to not be approach that most people wanted to do, but you can't say they provided no tooling.