IIRC, the primary driver for the move was, as you rightly surmise, financial. I think CX was another operator who did this. But whatever you may think of the detail of what this roll call of airlines does operationally, they don't really fall into the category of shysters of the aviation world.
There is a continuing fallout from this. After the move happened, airworthiness rules were changed to impose a maximum linear distance between adjacent emergency exits (60m?). This would stop any further door 3 sealings, because the distance between doors 2 and 4 would exceed that limit. But aircraft already converted could stay converted.
This rule bit Airbus when it was finalising the layout of the A340-600 (poss the -500 as well). Airbus also wanted to avoid having an overwing exit, but it would have breached that rule. They pressed for a waiver, but failed to get one, so had to install the overwing exits you now see.