Such languages are called "constructed languages" or "conlangs." There is a community of hobbyists who enjoy constructing them, learning them, and using them.
At one point, people seriously hoped that a well-designed constructed might become a universal global language. They even thought that having a universal language would lead to better global communication, and that better global communication might lead to world peace. They wanted to reverse the story of the Tower of Babel.
The first conlang to receive widespread use was called Volapük, invented in 1880. It may have had a million speakers at its peak. (Advocates of constructed languages often exaggerate the number of speakers). It declined rapidly.
The most successful of all conlangs has been Esperanto, invented in 1887. There may be as many as two million speakers today. There are a few cities in the world that have put up street signs in Esperanto as well as other languages.
Most conlangs start from scratch, using invented words. The idea is not to show favoritism to any existing languages and to be equally difficult for everybody. One of them, "Basic English," developed in the 1930s, uses English words--but with a restricted vocabulary of about 1,000 words and simplified grammar.
Interlingua, developed in the 1950s, was designed to be easily understood by speakers of the European Romance languages, with the hope that researchers would use it for publishing scientific papers.
It is my personal opinion that conlangs are a hobby or pastime. Some are obviously just hobbies, as in people who learn to speak Klingon. I suspect that people who are seriously interested in linguistics are tempted to try them.
Of course, some people honestly believe that by learning them and helping them grow, they eventually will become useful and make the world a better place.