Looking on the internet deeply has found these results:

this is why is the most popular phrase on the web.

that is why 16,620,000 results on the web	this is why 1250,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Dec 22, 2012 ... Is there any change in the meaning of sentence if I replace That is why with Which is why? For me both are suitable for the above context and�... "That is why you try and include everyone." "That is why you lock your doors when you leave home." "That is why she smiles when you walk by." "That is why you�... Mar 12, 2009 ... Uploaded on Mar 12, 2009. Official video of Jellyfish performing That Is Why from the album Bellybutton. Buy It Here: http://smarturl.it/9ekq8a�... That is why and which is why can be similar in meaning but function in different ways in a sentence. In that is why, that is a demonstrative pronoun. In which is�...	See, this is why I hate time. And this is why he died. We think this is why the ship jumped to warp. So this is why Prince Achmed stormed out. So this is why she wanted your laptop. See, this is why we're perfect together. Nancy, this is why it's funny... OK. See, this is why demons are better than people.

that is why

16,620,000 results on the web

this is why

1250,000,000 results on the web

More popular!

Dec 22, 2012 ... Is there any change in the meaning of sentence if I replace That is why with Which is why? For me both are suitable for the above context and�...
"That is why you try and include everyone." "That is why you lock your doors when you leave home." "That is why she smiles when you walk by." "That is why you�...
Mar 12, 2009 ... Uploaded on Mar 12, 2009. Official video of Jellyfish performing That Is Why from the album Bellybutton. Buy It Here: http://smarturl.it/9ekq8a�...
That is why and which is why can be similar in meaning but function in different ways in a sentence. In that is why, that is a demonstrative pronoun. In which is�...