Why UVM driver as non-blocking structure

[santhosh.vlsi]

Hi to all,

Can any one explain me

1. WhyUVM driver as non-blocking structure.
   vif.i_system_rdy <= duv_xtn.i_system_rdy;
   vif: Virtual interface
   duv_xtn: Transaction class object

2. why UVM monitor as blocking structure.

Regards,
Santhosh Kumar.