Agreeing with what the first comment said, but expressing the idea in different words, let's turn your question around and ask why TechCrunch posts should get to the front page?

A good-quality submission will be from a source with good content, close to original reporting of the facts, with some balance and sound judgment. Once in a while articles from TechCrunch fit those criteria, but much of the time there are better stories from better sources submitted to HN, and with luck of the draw in who is reading the new page at a given moment, generally better stories get upvoted, while average stories (frequent on TechCrunch) and below-average stories (not rare on TechCrunch) are ignored. I'm always looking for a pleasant surprise when I scan the new page

http://news.ycombinator.com/newest

(as I do several times each day) to look for stories to upvote. I try to submit stories that taught me something I didn't know before, as suggested in the Hacker News welcome letter.

http://ycombinator.com/newswelcome.html