enterprise geodatabase - ArcGIS SDE next rowid value doesn't increase at a constant rate

Using ArcGIS 10.5.1 and Postgresql 9.5 database, I created a point feature class named Locations. After I inserted 8 points in my Locations table, the objectid value of last row is 8.

An hour later, when I inserted a new point to the Locations table the object id value created as 408. But it should be 9.

Several hours later when I inserted a new Location, the objectid created 1220.

Why don't objectid values increase at a constant rate?