I wonder what kind of nut and bolt arrangement is used for the Plug?

Does it use

- Locktite (other brands are available)

- Second nut up tight against the first nut

- Split pin throught the nut and bolt arrangement

- Sping washer under nut

- Serrated washers either side of workpeice

- Lock nut with Nylon insert

People need to understand that vibration on a plane can do strange things to fixings as can the changes in pressure

Because you can sell a whole row of seats aligned with a plug bot you can't put seats aligned with a door. 
So the basic answer is it makes more profit for the airline. 
Companies exist to maximise their profits and cut every corner they can get away with to achieve that. 
Note 'get away with' is subject to laws, regulations, customer pressure, and in some cases ethics/morality

In the Max 8's there are seats next to the additional door (only two for passengers) and a jump seat for a crew member right next to the door. I had the 'pleasure' of sitting in that row recently with the crew member literally right in my face 

mapj1 said:

The slightly sad and worrying  thing here is that loose screws are not some high tech hard to grasp failure mode, and in a car or any other product would just trigger a recall notice.

In a newish car yes, but not in an older one - having had the brakes fail in my wife's car over Christmas, due to a calliper basically dropping off the car, something I'm very aware of! Whereas this incident, like all aviation incidents, will be picked over in huge detail for root causes, irrespective of the age of the vehicle. Hence I'm rather more nervous of crossing the road in front of 16 year old cars of a certain make and model than I am of flying in a 737...

(I'm not going to say what make and model as that would be unfair - could have happened in any car of that age.)

Loose screws are necessary if the airhostess is to be able to unscrew the emergency door quickly.  The H&S regulations need reviewing to be practical and safe for both crew and passengers.