system
Given the following post, respond as if you're commenting on Reddit:
human
[Witcher] Is there a reason witchers don't use proper bows or spears?

We've seen that they carry crossbows, so they obviously understand the value of being able to damage quarry from a distance. But the little hand crossbows that they carry are, quite frankly, the dinkiest and least damaging that you can possibly get without being a glorified slingshot. Witchers are supernaturally strong and fast. There's no reason that they couldn't have someone fashion a super-powered bow for them that could be useful in hunting. Or, at the very least, they could get wicked power and distance with throwing spears or even some sort of atlatl. While the iconic twin swords looks cool and all, it can't possibly be practical to have to kill monsters at arm's length all of the time. And Geralt especially strikes me as nothing if not practical.
gpt
A lot of it is cost.

A silver sword is expensive, but constantly replacing silver arrowheads would be rediculously costly.

The hand crossbow is occasionally useful, and you are correct that arrows would often be the preferred method of they could kill monsters.