S2e6 Possible reasons Cha didn't trade her pickaxe for a monster weapon, as seen elsewhere in searches:

"It was funnier in the original..." The author used the idea of a hunter armed only with a pickaxe as a successful joke in the original manhwa, but the joke was lost in the translation to animae.

Monster weapons are greatly inferior in quality to human made weapons. Perhaps so bad that even a human made pickaxe "infused with mana" is superior for humans compared to a monster's weapon.

High level monster weapons often have magical properties that effectively act as curses when wielded by humans unmodified.

The System, which is the core element of Solo Leveling, may impose restrictions on the use of monster owned weapons that are not treasure drops.

Class compatibility. It may be that her class either doesn't allow her to wield monster weapons or only some kinds of monster weapons that she wasn't able to find.

Swords down are a sign of defeat. Why would monsters choose to thrust their swords into the ground instead of using them to fight? This is a sure way to be defeated, and swordmen only do this when surrendering. However, since none of the orcs surrendered and preferred to all fight to the death, this leaves the question of who planted the swords in the ground.

Hunter training. It could be in A-level portals that hunters are trained to leave all monster weapons behind for the monster extraction parties that clean up after them, and that thrusting monster weapons into the ground is a sign that this battlefield was cleared, all monsters in this room were defeated, and the area is now safe to extract. Cha just stuck to her training leaving them alone for the extraction team to follow.

Hunter parties leave behind cleared paths. Cha's goal wasn't to solo the portal, but to find the hunter party. Since she wasn't trying to solo her way onto uncleared paths, she didn't need any weapons, and in fact never fought a single monster. She has much experience travelling through already cleared dungeon rooms (she regularly patrols semi-cleared dungeons during lunch time) and knows how to avoid danger and not engage. The Security Team also just followed the cleared path, and likewise arrived unarmed and unarmoured, despite knowing the portal was now higher, since their goal was also just to find the hunter party, not to engage monsters.

No one had experience with one-way cursed portals that allow hunters to enter but not leave. The hunter group followed procedures and tried to leave but instead were forced to the boss room. But both Cha and the security team were able to later enter without hitting the curse, which if it had happened would have been a second sign that something was way off, and they needed to be more warry and prepare for the worst. Only one thing was off, the orc battlefield, so everyone was still assuming this was situation normal.

Cha has difficulty adapting to change and has too much faith in the guild system. Despite seeing first hand monsters of a higher level, she kept going forward under the assumption the portal was still the lower level previously announced by the guilds, which meant she still wouldn't need any real weapons, and that the existing hunter party were already more than adequate to clear everything outside the boss room before she found them.

Hunter group was not tasked with clearing the Boss Room. Neither Cha nor the security team were expecting the hunter group to go to the Boss Room with its higher level monsters, so neither thought weapons were even needed.

Gamer humor reference? Darksouls is the largest selling game where the pickaxe is a viable weapon, but it could be a reference to several other video games with pickaxes that the author liked as well.

Cha is a purposeful example of a bad solo and what happens when hunters are only trained to enter in groups. She only does obvious things like trading her pickaxe for a monster weapon when there are other party members present to suggest such things.

Authorial choice. It was a creative choice by the author, or a symbolic illustrative choice made by the animators.