You know what I just realized?
It never says that
Ingwë,
Finwë and Elwë
were leaders before Oromë
took them to Valinor.
“Therefore Oromë was sent again to
them, and he chose from among them ambassadors who should go to Valinor
and speak for their people; and these were Ingwë,
Finwë and Elwë, who afterwards were kings.”
Of the Coming of the Elves and the Captivity of Melkor, the Silmarillion
That’s our introduction to them. The Vanyar, Noldor, and Teleri are described as the “kindred” of
Ingwë,
Finwë and Elwë
respectively, not their subjects. They certainly led those who undertook the Great Journey, but there’s no reason to believe they were the chieftains beforehand.
Why then were they the ones chosen as ambassadors? Because everyone else was terrified, and they were the only ones willing to follow the incredibly dangerous strange being, each for their own reason.
Ingwë
went because he saw the light of Aman reflected in
Oromë’s face, and wished to see the light in truth. He recognized the light as Good and Holy, and knew that the Valar would not harm him.
Finwë went in search of knowledge. Here was a being unlike any other known to elves, from a place likewise completely unknown.
Oromë claimed that the Valar would share knowledge with them, but even if that turned out to be false, there would still be much to discover.
Elwe went because he has a huge xeno kink. The presence of actual non-elf sapient beings, that unlike orcs wouldn’t try to kill him, meant that he had to check out Aman.