You may be asking, "But, Tamatha, bundt cakes are delicious, why do they have to be restricted to a specific season?" The answer is simple, when it's hot outside, the last thing you should be doing is baking something for a good hour.
Bundt cakes usually fall on the denser end of the cake spectrum, and therefore require long baking times. The warm days of late spring and early fall, and the freakin' hot days of summer are not the time to be heating your house from the inside! Also, I'm a fan of a more seasonal approach to cooking. When it's chilly out and you're all cozy, that's when you want a delicious slice of bundt cake. The summer is a time for delightful strawberry shortcake or a huge bowl of cherries or a sweet-tangy rhubarb pie baked by a friend (I'm afraid of pie crusts; I don't make pies). These things are all the more enjoyable because you don't have them all the time, but are, instead, reserved for certain times of year.
So that's why there's a Bundt Cake Season.