@arkandel Because there's more or less one enforced reaction to "I have stabbed you," if the roll to stab succeeds.
Think of how many different ways, "I cast a love spell on you!" ends if the roll to cast the spell succeeds, and how many examples there are in fiction of this going in very different directions than the caster intended.
None of that is new news.
The goals are different, and they're different stages, in a sense. Stabbing is one stage: stab, there is damage done. Love spell causing love is one stage. If the caster was content with the amount of interpretation that's left up to -- from slavish devotion to happy sex toy to possessive stalker -- that would also be a one stage goal. But that's not what people are typically trying to accomplish; they want it in the specific form they want and only that.
This is roughly on par with insisting that because you succeeded on your roll to stab that you now get to pick where the damage happened (without ever having to call a shot or take a penalty to hit or higher difficulty or whatever) and simultaneously sliced through the character's belt so their pants fell off and they mooned the crowd.
This is a not insignificant problem.