Men think only of utility when shopping; for them, though there is a premium, it's not about the brand but the quality. Once a man has bought something and found it handy, as long as the price isn't significantly higher than similar products, he won't easily switch brands even if it's a little more expensive the next time he buys.
When Zachary purchased a technique, it was much the same. Initially, he didn't think about the future when choosing a technique; knowing that the spells bought from the Scripture Hall wouldn't be a rip-off, he simply bought the least expensive one that met his needs.
Now that the technique has failed, it could be that the monster's body still has the ability to resist, or it could be the fish that didn't die and continued to nibble on the monster's corpse interfering with the "Universe in the Palm" technique.
Either way, it's not a good outcome for Zachary at this moment.
