SPARQL* DELETE/INSERT returning error when using nested triples within where clause

Question

why is it not allowed to include a nested triple like <<?s ?o ?p>> ?x ?y within the where clause of a insert/delete statement. It immediatelly returns an 500 error.

Following simple statement returns this error.

delete {
    
}
insert {
  
                                                           
} where {
<<?s ?o ?p>> ?x ?y.
}