Queen Chrysalis sees an opportunity to break up the Elements of Harmony before they spoil another one of her brilliant plans to rule all of Equestria. Since all of them are unmarried mares, all she needs to do is get them fighting over a stallion. And if one stallion isn't enough, she sends one male changeling for each of them, plus a spare.
Too bad she didn't think this one through first.
Editors: Tek, Peter
Vector credits: Wiki, Bocchinocullen (sign), Ackdari (changeling)