You vastly underestimate the time, manpower and money required to just switch to a new engine. Processes and work flows would need to be changed, adapting to a new engine would take too much time, customising the engine to suit the type of game the team would construct would take huge amounts of time and thus, money.
Starting a new engine from scratch took Kojima 5 years a $100 million bucks. Then he had to create the game which then took another few years and probably another damn $150+ million, and so Im not surprised Konami was damn pissed at the guy. MGSV released 7 years after MGS4...
Or you could look at CDPR, they tried to customise and upgrade their engine at the same time as developing the actual game and we know how that turned out.
There's a reason developers stick to the same engine for decades, like Bethesda and Activision. Besides people play From games for the game design, gameplay, atmosphere and world design.
The movement in Bloodborne is just so satisfying, so I agree.