The same argument could be made for any arbitrary amount of time though.
1 week is not enough
1 month is not enough
1 year is not enough
5 years is not enough
10 years is not enough
20 years is not enough...
Do you really have Python projects that can't be migrated in 3 years?
At some point the line has to be drawn to move everyone forward. Extending the EOL for the last long-term of 2.7.x by 5 additional years is pretty generous.