The time that took to be accepted Galileo was right about the kind of relationship between the earth and the sun makes a question about the reason! Was it a political reaction by the Pope to be more popular or a symbolic reaction by the church to try to compensate its dark history or not a real reaction that had not happened before because of church's doubts?
Many volumes have been written about Galileo and the Church, and so an answer on this site cannot do the topic justice. But despite the gleeful reporting by critics of the Catholic Church, the 1992 report was not about astronomy. It was an admission that Galileo had been mistreated and wrongfully convicted.
Soon after his election in 1979, Pope John Paul II appointed a commission to review Galileo's trials. Thirteen years later, as reported in the Los Angeles Times:
Second, a 1984 preliminary report from the commission suggests that Galileo's 1633 trial was prosecuted on a forgery. To simplify, he was accused of violating a 1616 decree that banned him from even discussing the theory. It now appears that the decree entered as evidence was not the same document he had agreed to, and one that was much more restrictive. Galileo was a genius, but an arrogant genius: he had made enemies in Rome.
I would note that heliocentric theories date back to the ancient Greeks, and while Copernicus attracted many critics, both Catholic and Protestant, the Church did not attempt to ban his books for six decades, until they got swept up in anti-Galilean sentiment. Consider also that Galileo's complete works (accompanied by letters stating the Church's criticisms) were published in 1741 with papal imprimatur, and the proscription against them was lifted in 1757, not 1992.
To add to choster's excellent answer, don't forget that Vatican was an intensely political place (then, just as ever). It didn't help Galileo's case that he took the Pope who previously personally supported him:
... and basically personally insulted that Pope. In print! (by putting Pope's caricature as an idiot character named Simplicio)
Even then, Galileo was strongly supported by one of the 10 judges in the trial, Francesco Barberini - who was none other than Pope's nephew and elevated to Cardinalship by Urban's nepotism.
Additional factors that forced Urban's hand, as choser's answer alluded to, were due to European religious and political landscape. At the time, Vatican was in the midst of dealing with Protestantism on one hand, and attempts by Spanish Hapsburgs to subjugate vatican to Spain on the other. The latter was critically important - any appearance of deviation from orthodoxy would strengthen the Spanish hand.
As a reminder of the struggle with Spain, recall that Urban was nearly deposed by Spanish Cardinals in 1636