I've noticed that, besides for the several masechtos actually a part of Shas Bavli that don't have Gemara (shameless plug), it's the custom of printers to include Mishnayos Zera'im after Brachos and Mishnayos Taharos after Niddah. Both of these make sense; if they want to round out the Shishah Sedarim, they might as well include those mishnayos in a volume with the one Masechta that actually has Gemara.
My question is the Masechtos Ketanos. A collection of Braisos, these masechtos cover a wide range of topics, including Mezuzah, Sefer Torah, Simchos (a euphemism), Kallah, and Derech Eretz.
If printers are going to put them in any Seder, why Nezikin? It's not the beginning of the Shishah Sedarim, it's not the end, it's not the middle, and it's not the same topic as just about any of them. Why not put them at the end of Shas, or split them up among the six orders by which ones fit the general topic - Kallah in Nashim, Simchos in Moed, Derech Eretz in Nezikin (to keep Avos company), etc.?