Because the majority play team games whre strategy and skills are of utmost importance. 1v1 is just about a regular build order or reliance on some op units or P2W.
Team games are now broken thanks to the constant efforts by relic during the past year to make the game the way some "top" players approve of.
Let's deal with the truth, no one plays 1v1, and team games are broken as hell.
Apart from just being wrong saying no one plays 1v1, balancing the game around anything more than 1v1 or possibly 2v2 is not practical, there are too many variables in those modes.