Baffled

Went to do a quote on plastering a living wall. Piece of p**s i thought. The client explained the previous plasterer only put one coat on 3 walls. The 4th wall had no major defects and was plastered with bonding, scratched then primed. I asked why the previous plasterer did this and the client didnt know. Before it was bonded it only had matt paint over plaster board.
So my question is why would you use bonding plaster scracth coat and prime the wall over matt paint? Why not PVA it then 2...

Baffled