All I know about it is that the advent of mechanized armies killed it. I don’t entirely understand how. At least to me, it still seems somewhat practical to have a trench, as it seems like it would still offer some decent protection.
A now-deleted user offers a comprehensive treatment in this thread, and u/jonewer has input in this thread.
I should also note that a trench line is simply the logical evolution of the various forms of defensive fighting positions (foxholes and similar such), which are still in use even today. You can even read the US Army's Field Manual 21-75, whose Chapter 2 covers just such positions. What has changed are the conditions that led to the rise of the extensive trench lines of the Western Front.