What Jewish revolts occurred in Jerusalem (during the Roman occupation) before 33 AD (about the time of Palm Sunday)?
And letting them have the parade would show the Romans just how much support Jesus had, and who were his big supporters. Better for everything to be out in the open so you can get easy and free information than to not know what's going on in secret. They could always bring him in at anytime. Also, preventing it might have caused more ill-will than allowing it. And there doesn't seem to be any writings of people saying, "Hey, wait a minute, I'd don't remember any big parade in Jerusalem 35 years ago." Or even "Hey wait a minute, I don't remember any guy name Jesus raising the dead or doing over 30 other miracles".
Akhenaten has already mentioned Judas the Galilean. Here's another uprising. In
Antiquities of the Jews, Book 18, Chapter 3, item 2, Josephus tells us that Pilate used temple funds to build an aqueduct to bring water to Jerusalem. A number of Jews - Josephus says many ten thousands - massed and protested the appropriation of temple funds for a secular project. Pilate told them to disperse. When they refused to do so, he gave a signal to Roman soldiers dressed as Jews and mixed into the crowd, who were carrying concealed weapons, and these soldiers killed and wounded many of the protesters.
Antiquities Book 18, Chapter 4, item 1 tells of another potential uprising, this time among the Samaritans. when an armed multitude of them gathered in a village at the base of Mt. Gerrizim, Pilate sent troops of cavalry and foot soldiers to attack them. Yet, according to the gospels, we are supposed to believe that this brutal man was cowed by a mob demanding that Barabbas be released and Jesus be crucified.
BTW, you still haven't explained why, in a few short days, the crowds welcoming Jesus had dissipated and another mob had assembled to demand his death. It's also odd, in the incident of Jesus blasting the fig tree and his driving the money changers out of the Temple, that he seems to be coming from Bethany to Jerusalem and back again on a regular basis without attracting any attention, either from crowds crying out, "
Hosannah," or from the Romans. The Palm Sunday crowds seem to have forgotten Jesus rather quickly.
As to people writing about Jesus, denying what was written in the gospels, you must remember that supernatural claims were quite common in hose days and likely to be shrugged off - just as Justin Martyr shrugged off those who claimed to have seen deceased emperors ascending to heaven in the smoke of the funeral pyres. You also have to remember that, at the time the gospels were written, between the years 70 and 90, nobody but the Christians were interested in such claims. Others would not be reading the gospels and wouldn't have bothered with the claims of a small heretical sect. Finally, you must remember that the gospels and other books of the New Testament were written in Greek for a culturally Greek audience. Paul's epistles, which antedate the gospels, were written to congregations in western Asia Minor (Galatians), in Greek cites around the Aegean Sea and in Rome. This audience would have been largely ignorant of the laws and customs of Judea (as the author of Mark was), as well as being ignorant of what did or did not happen to a minor messianic pretender - one who was scarcely mentioned (if at all) by Josephus.