conversion lujvo

[BestATN@aol.com]

why are lujvo of converted gismu preferred over the bare converted gismu?
e.g. why is [selcasnu] used instead of [se casnu] in the nuzban headings?  it 
seems to me that [se casnu] should be used, since it's simpler and its 
component words are basic ones.  
steven lytle