Considering that weapon upgrades require 2, 4, and 6 of the same material for each set of 3 upgrade levels, I suspect that From Software made a relatively late decision to double the amount of materials needed for most upgrades.
that's another thing that was added just to annoy players.
DeS: the game gives you a bunch of different stones which may seem confusing at first, but it actually diversifies the gameplay since player is incentivized to use different weapons and the game sometimes drops already upgraded and infused stuff (like crescent falchion for example).
Dark Souls: early enemies drop titanite shards, plus the first blacksmith already sells infinite amount of them, allowing player to upgrade any weapon to +5 to try out different movesets
Dark Souls 2: infinite titanite is gated behind story progression, but the game gives you enough to keep 2-3 main weapons upgraded. Plus now there's a minor decision to be made - do you want to use a newly found titanite shard to immediately upgrade backup weapon to +1, or do you want to continune looking for materials to upgrade the first weapon to +2/+3?
Dark Souls 3:
oh, a titanite shard! ...aaand i can't do anything with it, at least until i find another one.
and now Elden Ring makes upgrading even more annoying.