Those same experts say that 95% of the scrolls were written by persons outside Qumram and many of the scrolls date before the Qumram community took over the settlement.
Simple destructive reasoning can achieve a great deal. The first thing that must be done is to remove all preconceived ideas that the Qumram community did all the work, then consider the distance of the caves one from the other. Also to be considered is the vast number of differences in the scrolls. Close the debate about who wrote them, the Essenes, or Sadducees, or any other group. Also drop the assumption that only the Essenes occupied the area as ones who hid scrolls.
So what does that leave us?
Since every bit of speculation from the experts is based on their ideas and interpretions and not on fact I will do likewise.
1) We already know that at the time of Judas Maccubees there were several Jewish religious factions and several were fighting for control of oversize of the Temple. So one or more groups is outstead and they settle at Qumram. They have a few Biblical manuscripts and they write their own books. They also come across some Jewish lliterature and keep it. During this time ones come and go. The group finds a few caves and they use for storage. Soon the group dies out or is absorbed back into the Jewish mainstream. As other groups are accepted and rejected they too find this place and likewise leave their deposits.
2) It is also very likely that some Jewish priest believed the Christians and Jesus when warned about the Romans coming the first time in 666CE. The Greek Scriptures are clear that some of the priest accepted Jesus as the massiah. So logically they may have convinced family to leave Jerusalem when the Roman armies withdrew in 66. Since the Jews did not want to mix with gentiles they would have gone to known hiding places. Qumram being a well known place some logically would have gone there and found different caves in which to hide scrolls. They may have even used caves that had scrolls already in place thinking others hid their own. Fact is many of the scrolls can't be attributed to the Essenes so why force it, logically some were hidden from the Romans in 66 CE.
3) Still yet, what of the non-biblical scrolls with Biblical overtones? Ezra has basically set the canon of the Hebrew Scriptures about 160 years earlier. Now the Maccubees have their fight with the Greeks and later the Jews with the Romans. So here you are, an unknown Jew sitting at a table wanting your 15 minutes. Ah write a book with Biblical overtones and apply prophecy to the Greeks or Romans, place it in the cave with Daniel and Isaiah and maybe it will get added to the canon. To assume that there were no Jews with personal aspirations for fame is to ignore the Greek Scriptures. It is likely some of the scrolls are simply a man of his day leaving his mark. Today wedo it with YouTube, or some form of Social Media, well writing a religious book was the Social Media of that time. Make it good enough and maybe, but in the end it was God who set the final canon. But experts debate all those other scrolls.
4) It could also be that some scrolls were religious startups that failed.
In the end the Essenes wrote only about 5% and they may not have known of the existence of the other scrolls or caves. The others were likely deposited by Jews on the run from Romans, some scrolls may simply have been one priest trying to understand the Law in his own manner.