Tcp – Is ping in the application layer

Of course you can directly interact with the IP layer. The question is not about "why you can't", but about "why you wouldn't want/need to".

Since you mention higher level languages, the reason why they exist is the same as the reason the transport layer exists. A higher level language makes things easier by providing abstraction. You can code your application in an assembly language, but you will be spending a lot of effort on problems that have been hidden by higher level languages.

Most applications will benefit from a network which provides features like process identification, reliable communication, in order delivery or flow control. So it makes sense implementing these features once in a standardized protocol, instead of having to include custom solutions in every application.

There are situations in which designing your own solution can be beneficial or even necessary, but in most cases using TCP or UDP will just work and save you a lot of hassle. Doing it yourself can also be very educational and make you appreciate the work that has been done by others.

There are quite a few global networks other than internet, mostly used for scientific research or military / diplomatic needs. They may or may not use IP as the needs of their users dictate.

For example, you can find the current map of the Global Lambda Integrated Facility (GLIF) here, which is one such network.

Internet2 is also a separate initiative, and while the primary Internet2 network is focused on North America, it is interconnected with similar networks in other countries.