Bitcoin is an open source project; its codes, which contain the rules and the logic of the network, are free to use.
We can analyze the code, actively participate in its modification and in the correction of any bugs, distribute it, copy it and modify it, even realizing our own version of the system, not compatible with the Bitcoin network rules.
Parallels can be made with other well known systems: Bitcoin is open source as Linux and Android operating systems, in contrast to closed proprietary systems such as Microsoft Windows or Apple iOS.
Technically, Bitcoin is not owned by anyone but by everyone.
Being an open source project is one of the fundamental features of Bitcoin: you don't need to trust the system or who created it. With a little study or a professional, you can analyze the code and make sure it actually does what it was built for.
The system is reliable precisely because it does not require trust. It can be defined as a trustless system.
I understand that it is difficult to imagine that a system that has gained so much importance and has made its monetary unit take on so much economic value, is both free and in the public domain, but indeed the concept of proprietary software, in the history of computer science, came along much later than free software.
Since the beginning of the development of computers and then of the Internet, the technology has been freely accessible. Indeed, this very freedom has fostered its rapid spread!
Bitcoin is no different.
Developers working directly on it do so in a spirit of collaboration, just like those who, at the dawn of the Internet, worked together to create shared rules and protocols.
So where is the profit?
The system by itself does not allow us to earn, but this does not mean that applications cannot be built on it and that therefore the developers do not receive their legitimate compensation. Anyone, a single individual, a company or even a state, can build on Bitcoin, and can do it voluntarily or on payment, just as those who build on the Web can have their own economic advantage.
Think about pay per view services like Netflix, created thanks to the Internet, free and open source system, or "free" services - you actually pay for their use with your data - like Facebook, whose developers are regularly paid and in some cases even handsomely.
