It's not even that no list uses 3 Decimators.
It's mathematically impossible to run 3 Decimators in a list.
Therefore, even those of us who are really compulsive about buying 100 points of every ship won't have 3 Decimators.
And even if they change the point costs of Decimators to allow us to run 3 of them in 2.0, people who want to do so will need to buy a new Decimator (for the plastic ship), and so won't have any use for the 3rd conversion.