Well, that's either something the author didn't think of or something they weren't all that concerned about. I would guess that most players build things for themselves or give away less valuable picks to other players who are starting out. I wouldn't hand over my prized pick for someone else to use. It's mine! I can't remember fully but I think Iguana tools are split between experience and boosting? It would make sense that the experience related modifiers are per player for a given tool. I'd like to see that added.
Oh yes, I 'will' complain
I noticed the extra modifiers but you can't blame me for thinking that some of the random extra bonuses on the tool I've spent hours building can be detrimental to what I'm actually planning on doing with the tool. Example: I specifically crafted a 'cleaver' because it's supposed to be better at removing heads (yes, there are other ways but I wanted to try 'this' way). I started using it on Endermen and it went fiery. Now that sword is useless for removing Endermen heads. Can I work around it? Yes, of course but it still seems like an oversight that a tool whose stated special ability is head removal now can't remove the heads of a specific mob.