She may have assumed that you did not want to cum at that point in time. Many customers see blow job as foreplay and if they cum too early without having the main course and many other things, they feel frustrated, especially if it's a 1hr session.

Experienced WL can sense if you are close to the edge and slow down to "help" you to control. If you tell her that you want a CIM NOW I think she would happily accommodate and go all the way.

I haven't seen Subin but I have WLs do exactly the same thing for above reason.