Can one of the gameplay devs answer this question about junglers and masteries?

Since riot reworked the masteries this preseason, is there a reason you guys didn't create a fourth jungler's line with a upgraded smite as one of the options? Why have the item you buy change your smite, instead of something like a mastery (or a new smite summoner spell)?

If anything, the new decisions that the mastery system is evolving into kind of beg for something like this.