Why did this cake fail?

Batters full of starches and sugars are always sticky, how you prevent it from sticking partly depends on the plan. Some pans have coatings which while called non-stick aren't, but do reduce sticking somewhat. On pans like these often buttering is sufficient, and 'normal' cake pan shapes allow you to loosen the sides by running a knife around the side, so even if they stick you can free the cake. Putting a piece of baking paper on the bottom of a flat bottomed pan is a sure-fire way of preventing issues.

When you have an odd shape like a bundt, paper won't work, and you can't afford anything sticking, so the best way to ensure it frees is to generously butter (not oil or spray) the pan and then flour it. You can also make cake release, which can be sprayed or brushed on, using equal volumes of flour, oil and shortening.