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This easily could have been the title of an article bashing python fragmentation

This was also my first thought. But with changes as big as Python 3, there is probably no way around this.

How does that explain the four "current" versions, then?

Security releases are for old distros/users.

There aren't 4 current versions, there are 2. The other 2 are old versions that still get security updates.

Security updates are always backported, this is how Linux distros operate.