Jesus did not state why the Spirit would not come until He went back to the Father, but He clearly taught that His sacrificial work on the cross was necessary before the Holy Spirit (Counselor) was to arrive on planet earth.
If you love Me, keep My commandments. And I will pray the Father, and He will give you another Helper, that He may abide with you forever.
Once again, if you will notice, the Holy Spirit only comes to those who are obedient to the King's Word. They are the ones to whom Jesus will send the Holy Spirit (Counselor, teacher). But the Helper, the Holy Spirit, whom the Father will send in My name, He will teach you all things, and bring to your remembrance all things that I said to you.
You must live by the King's Word, which are His standards--principles and laws.
John 16:7 John 14:15-16 John 14:26