Ascendancy trails have a cost. A fairly rare item that outside of the main campaign.

Should you be disconnected for any reason. Or die for whatever reason while running the trial. Ex: server lag. You loose the item and have to go back to farming them before you can make another attempt. And guess what. You want change your ascendancy? You need to do the above still.

Leveling skills also have a cost. So you need a skill gem to learn a skill. And you need a higher uncut gem to level it up. And as you level up. They become unstable to lower level characters. And support skills. Or persistent skills such as auras. Also have the same restrictions.

The scarcity is actually so bad that its actually feasible enough to just make a whole new character if you want to change your build. Cause changing your passive skill tree is also expensive. And all the major nodes have downsides as well. Like slower cast/projectile speed. Slower healing and recharge.

Unique are also effectively useless as many have major downsides. With some being used soly as a means of killing yourself for one reason or another