Why? Because market leaders are wedded to an existing paradigm, to caution and convention. And so, they focus on incremental changes in their served markets to stay a step ahead of the competition. They don't innovate for customers. They tweak their offering to try to beat the other guy.
Mark Twain once wrote:
"The best swordsman in the world doesn't need to fear the
second best swordsman in the world; no, the person for him
to be afraid of is some ignorant antagonist who has never
had a sword in his hand before; he doesn’t do the thing he
ought to do, and so the expert isn't prepared for him; he
does the thing he ought not to do and often it catches the
expert out and ends him on the spot."