Good question. Here are the facts:
As some of the other posters have written, we (jews) can only offer sacrifices in the temple. So, no-temple; no sacrifice. This is a law which was given to us by G-d to be enforced once the temple was established.
To those very ill-informed posters who said "it's because of jesus etc..", I have to bluntly say they're wrong. Firstly, we don't believe in jesus etc.. He's got nothing to do with it. Secondly, Jesus is supposed to be a sin sacrifice (or passover sacrifice; it seems christianity doesn't have that straight yet) -- but there are LOTS of other types of sacrifices! So why would those other ones end just because of jesus? The answer is clear: It has nothing to do with jesus.
And lastly, since I assume the questioner is most concerned with sin sacrifices, it is appropriate that I point out that judaism has *never* considered sacrifices as being the important ingredient in atonement. Rather, heartfelt repentance is the main part. Sacrifices, prayer, charity -- all the externals associated with atonement in Judaism -- are all secondary and certainly wouldn't hold back atonement.
As it says in Hosea 14:3, "Take with you words, and return unto the L-RD; say unto Him: 'Forgive all iniquity, and accept that which is good; so will we render for bullocks the offering of our lips."
cheerio