Why are large blocks of numbers skipped in sequence?

We're are on Oracle EBS 12.2.10. We have a Apex program that inserts data into a staging table. There is a database trigger that uses a sequence before insert into the staging table to generate an ID number. The sequence is setup to increment by one. I did a test where I checked last sequence number in the sequence, loaded a file with 6877 records then checked the last sequence number again. I had expected to see the next sequence number was a number 6878 higher than the one before I started. But