What they pay big money for
In my opinion, the reasons why they can pay a really big salary are two - responsibility and qualifications. It sounds somewhat abstract, so I’ll explain.
Responsibility
If the operation of any system is critical for business, then the person responsible for the smooth operation of this system, taking responsibility for its work, should receive more. At the same time, it is quite possible that in the event of any failure (even at 3 a.m.) - optionally, but possible - he will have to break loose and go to deal with the problem. But the authorities know for sure - they have a guarantee, the person who is responsible for this. And, as you can see, there is no need to do more for this.
Qualification
I think that we all understand that not one hundred projects were ruined by the armlessness of the people working there - somewhere, something is not connected there, but nobody knows how correctly, it is crookedly made up and everything goes around in the explorer, the code is not object-oriented and making changes there is hellishly difficult. And there must be a person who does this accurately, correctly, and scalably. Otherwise, in the end, nothing will work. For example, many companies have employees who are engaged in optimizing performance and improving system performance. Giving him some deadlines is stupid - “After 2 weeks, you should increase productivity by one and a half times, otherwise we will fire you!” Most likely, such people receive bonuses in case of particularly serious achievements, but otherwise they are given a quiet job. Well, quite possibly they share their qualifications with other employees - for example, they help write immediately more load-optimized code. And as you can see, here too, you do not need to do more.
But often this separation is somewhat contrived - often these two reasons go hand in hand. The greatest money is paid to those who say "I know how to." I know how to make project attendance grow 10 times. I know how to increase profits. I know how to grab a large piece of the market. Such people are given a sufficient amount of resources - money, working hands, because the leaders know that all this will pay off with interest. That the large costs of such an employee will lead to even greater profits. And just such people in the business environment, in any field, are worth their weight in gold.