It's lacking an endpoint, or aspirational goal, or loop, or some other reason to keep a player engaged for a sustained duration of time.
There's also no reason to keep knives, so instead of having an inventory, why not auto-sell and convert the inventory to a Crafting History; just add a "Sort by acquisition" option and auto-sort to whatever the player has most recently set when opening it.
Alternatively, there could be some benefit to keeping certain knives; perhaps a Glitch knife could increase the sale value of all knives, or Eternal Knives could increase the Multi-Hit chance or something.
Speaking of, considering there's seven rarities, it feels strange to pull a Special (Glitch) or Eternal considering the only benefit is higher sale value; if you're going to have hidden rarities, there should be some update to the UI to acknowledge that the player has pulled them afterwards.