Because thats not how it works! You don't start from scratch, you simply swap out perks. So if the meta changes or your playstyle changes, you can simply swap out the perks for some materials. I just did this with my glaive so I know you don't lose progression. I changed all perks and lost no progression. Leveling is fairly quick depending on events.
I think the system needs some work like higher caps for materials, 250 seems stupid. Overall I think there is lots of potential.