The Qomar system was strictly regulated, as they were highly xenophobic, not for fear or war reasons, but the Qomar believed they were superior to many other races. Simpler species' scanning beams were so incompatible with their technology, that they could even disrupt their propulsion systems. The space around their planet was very busy, and simply navigating the many ships could be troublesome.
In 2376, the USS Voyager visited the Qomar homeworld when they were invited there, after The Doctor had introduced several of their species to music. After The Doctor had performed a concert for Prelate Koru, he was invited to sing in front of hundreds of people on the planet. They completely remodeled one of the many lecture halls on the planet, so that the shorter than average Qomar could see him on the stage.
After the performance had been transmitted to hundreds of millions of people on the planet, The Doctor became a star, and received "fan mail" from many of them.
The Doctor almost decided to stay on the planet, but in the end, he remained on Voyager when Tincoo created the Qomar singing holographic matrix which she and the other Qomar considered far more superior though it possessed only more advanced vocal capabilities and lacked the talent and soul that The Doctor possessed. (VOY: "Virtuoso")