You didn't ask about Hit Spells or anything else.
You asked two questions:
1.
What's the thought behind this? Subjective, asking someone here to give an answer to what some dev was thinking prior to release of AoS.
2.
Why can't FC1 or SC be applied to a weapon like hit spells are? Also seeking a subjective interpretation or guess at a possible reason the developers did what they did and not what you may think is a better idea.
I answered, giving my thoughts as to why they may have done as they did, namely that it is possible they thought giving a crafted weapon the potential for three positive mods, in respect to mages in particular, couple with the ability to cast spells while equipped with the thing, may have seemed to them at the time as far too powerful.
You didn't like my guess, fine, take on someone else's guess...or make your own guess...because the real answer to both your questions is....
Who knows, It's anyone's guess, n'est ce pas?
Oh and, for the record, Spell Channeling, Mage Weapon & FC1 would be, in fact, 3 mods as I said, and if you add the other 2 possibles from crafting with a val hammer, that does equal 5.
Accepting, of course, that Damage Increase is not a mod, but a crafting bonus not dependent on the use of any special hammers or tools.
Now I'm not trying to get into a fight with you over this, I did however take some exception at your reply to what I considered a reasonable answer when you questioned whether I had even read the OP and added a *sigh*