I used to be of that mind. And I see how it makes sense, but realistically, how often is a magus going to actually do the craft, pursue the craft, study the craft and perform the craft. Ultimately it takes time away from magic development. It can make sense for some characters that derive a substantial benefit from a strong Crafting skill, like Verditius, but I don't think it makes a lot of sense for a Rego Crafter in the long arc of the character.
How would you quantify that bonus? If we treat the bonus similarly to how Magic Theory is used in Magic research, it's a cap of +3, and you require a ridiculously high Magic Theory score to get that bonus so for Crafting you need a ridiculously high Crafting score. If you divide the Crafting ability by 2, perhaps, the bonus for someone who is pretty well trained at 6 (a professional) is only +3, which is simply an Ease Factor, in exchange for 105 XP. 105 XP is a lot, if we start from zero and assume 10 xp per season, it takes 11 seasons to get to that level. Granted characters being generated can plunk down 105 XP, pretty easily, but that's a substantial portion of the total XP, and competes against other abilities and Arts.
I've been thinking about this issue for a while, and all adding an ability to factor into the EF for any crafting does is force the magus to spread himself out, and not dive deeper into magic. One of the things I'd like to see, hearkens back to something Timothy Ferguson wrote, but I can't find, about Art scores representing knowledge in mundane abilities. I dislike that for several reasons, but have been thinking about having spell levels add up to a derived ability score. If you have 75 levels of stone spells, you have an effective ability score of Stonecrafting of 5, or something. But, it's not polished, or even deeply thought at this point, more of a wisp of an idea.