Assuming an airline has to have airworthy acft and qualified and apt crews, acft ageing and appealing cabins contribute for a good customer service from the moment the pax buys his/her ticket according with the pax's cheap or expensive form of affordability. And this includes keeping promises according with loyalty programs, timely flight information before the flight, check in, baggage handling, in-flight care, etc.. They all play a major role in attracting and keeping business. This is planning.
However, there are disruptions and it's here where most airlines, here and elsewhere, fail to demonstrate their ability to minimise the inconveniences and by not keeping pax properly informed. The preference is to lie, buy time till someone finds out a piece of different information. True or not, that rumour spreads around like a fire in a fireworks warehouse. Now, it's out of control, and sometimes because of little money some manager refuses to pay. No big picture.
Staff is poorly trained to deal with the disruptions and passengers get obviously angry. You cannot buy experience cheaply. You'll not get experience if there is no periodic and professional training, retraining, line-checking, de-briefing, etc.. Line checking is also applicable to ground staff.
The service quality can only be seen when you are there, dealing with the problems and not getting 100%s in classrooms. Also, IOSA and other certifications are so nicely and conveniently handled that they keep in place ever looming deficiencies. But top management is very happy and makes press announcements feting the occasion.
The root causes are very diverse. It's poor management, training, self-accountability, evaluations, government interference, etc..
I noticed that in this part of the world, a lot of poor management derives from lack of real-time experiences and ends up with autocracies where it's the boss' ideas counting and no other, without going down to "the floor" to look for feedback and sometimes revealing ideas from the line guys.