Why have Jews stopped offering sacrifices to atone for their sins?
The sacrifices only ended because the Temple fell; the Romans
destroyed it in 70 CE. Jews are not allowed to offer sacrifices
anywhere else (Deuteronomy ch.12). Also, in Judaism the sacrifices
were only for unintentional sins - and they were never the only
route to atonement. They were used primarily to draw us closer to
God. The sacrifices were a consequence of committing a sin (not all
sins, might I add), but not meant to completely atone for one's
sin. The sacrifice was used so that the Jew would see himself in
the animal and realize that because of his sins, it ought to be him
who is being offered up, not the animal. In order for the sin to be
atoned for, the Jew needs to do teshuvah (repentance). This
consists of several things: regretting the act, saying that you
will never do the act again with all intention to follow through
with this, and never doing the act again.
No one today has authority to perform the sacrifices.