Every operating system has to question itself, what a potential alternative is. Linux is not an exception, it make sense to ask which kind of software is available which has a different philosophy and works better. The amount of alternatives is very high. They have to common principle in mind. The typical Linux competitor is bundled with hardware and it's sourcecode is closed source.
Let me give some example: Mac OS X, HP-UX, AIX, Sun-OS, VMS, Windows 10 and many more can be categorized as Linux alternatives. The reason why these operating systems are better is because they are fullfill the need of the hardware manufactoring company better. Let us take one example of the list which is HP-UX and ask why this operating system was developed. The reason was, that the company HP has developed a new hardware architecture and to sell the system to the customers they need an operating system on top of the hardware. Calling this operating system “unix like” doesn't describe HP-UX very well. Because the idea was not to emulate Unix, the idea was to educate the consumers in a certain way. The main idea behind HP-UX is, that the customer is not allowed to use any other kind of software. Even he owns the hardware, he is not allowed to replace the operating system with something else, because then he will loose the warranty.
The interesting question is, why did HP developed HP-UX? Why did they not used an of the shelf FreeBSD system which will run great on the hardware? This question is hard to answer. We can assume, that HP was not the only company who made this decision. Microsoft, Apple and IBM also decided to invent the wheel twice. They all have programmed their own operating system which fits to special hardware and they not used existing software. One possible explanation is, that this kind of extra work is the business of these companies. Apple for example has a large software development department, their job is to program lots of sourcecode. Suppose the software departmant contains of 5000 programmers and they would decide not to write a new operating system but use code already written by somebody else. Does this fit to the need of Apple? No, it won't be a good idea. From the perspective of Apple, HP and many other companies it make sense to programm their own operating system which runs only on their hardware. In the next step the customer is forded to use this software and the company can educate the customer, why this program is great.
We can say that in the software industry it is a common principle to rewrite existing code. That means, the companies are doing extra work, if the problem was solved by somebody else in the past. That means, HP writes his own file system, Microsoft has written it's own filesystem, Apple too and IBM also. And all of these programs are sold to the customers. As a result, the price for software is high because so much energy was invested into the product. It is some kind of individual product which was taylored to a concrete product. It's important to explain, that not the customer has an advantage but the company how made such programs.
From the perspective of the customer the ideal world would contains of only one operating system under which every programs runs out of the box and which is available for free. This is equal to a customer paradise. Computer companies have no motivation to build such universal operating system because they won't earn much money in this market.
Now we can answer why Linux is special. The first feature is, that Linux runs under every hardware. No matter if it's a PC, an Apple, a server or a smartphone, Linux runs everywhere. The second issue is, that the software is delivered as open source. The combination of both is ideal for the customers but it's a nightmare for the hardware companies. Linux is something which is not wanted by HP, IBM or Apple. Linux is some kind of standard which fits to the need of the mainstream customers. And exactly this is the reason why Linux is hated by IBM, Apple and other. Because the interests of a company are different from the needs of the customer.
Let us analyze the market share of Linux. Technically it's possible to install Linux on an IBM mainframe. It's also possible to install the operating system on an Apple computer. In both cases, the customer will profit from it very well because he no longer dependend from the underlying hardware. But let us focus on the needs of the hardware companies. What is the feeling of IBM if the customer prefers Linux? What will Apple say, if the enduser is installing Ubuntu on the iMac? In both cases, they are not amused. They will forbid it either by technical restrictations, because of warrenty problems or with indoctrination. They are trying to convince the customer to behave in a certain way. Or to explain it from the other point of view. if the apple user will install Linux on Apple hardware he will feel guilty, he has done something which is wrong. The relationship to the Apple company is broken.
Most customers are in fear of such a relationship. They want to become the friend of the hardware company and as a consequence they won't install the Llinux operating system. They are doing so because their position is weak. They are not informed very well about the technical side, and they are in fear to make something wrong.
Some youtube videos are available in which an enduser has installed Linux on an Apple computer. But this is done only for outdated computers and mostly the customer feels badly. The reason is, that he has done something which is against the interests of the Apple company. Using Linux on a computer is equal to become the king of the hardware and ignore the hardware company.