"Why is it so hard to stand flat en pointe?"
First of all, when a student asks me this question, she usually means that, when she comes to center and has no barre to hold onto, she starts to wobble on her leg, especially when she shifts from two feet to one, as in a developpe.
To be sure, pointe shoes are not slippers. They are not as pliable, not as supple, not as form-fitting. They do not cover your feet the way flat slippers do. There is a thin strip of leather against the floor and thick cardboard under your foot. It only makes sense that it's harder to balance on one leg when you are wearing them. If they are broken in a bit, they are somewhat softer and a little easier to wear and stand in.
But the bigger issue has nothing to do with the actual shoes. I recommend tackling wobbly legs in the following ways:
1. Start with your core. Hold your abdominal muscles and your back muscles, pulling them up on both sides of your spine, front and back. Do not hold your breath but be sure to stay lifted, as if you have a partner holding your ribcage up and out of your pelvis.
2. Engage your upper back muscles. Always consider your port de bras, the carriage of your arms. By feeding energy from your spine out to your shoulders, biceps, triceps, forearms and fingers, you will balance out the lower torso and feel more suspended.
3. Keep the pelvic bones tilted up. If your hip bones are the base of your tray of snacks, don't tip the snacks into someone's lap!
4. Engage both your quads and hamstrings. In much the same way as your core muscles are being used, pull up both sides of your femur, which will in turn keep your kneecap lifted and stable as well.
5. Lift your arches. There are 3 arches: medial (the inner arch and the biggest), the lateral (the outside of the foot) and the metatarsal (the top of the foot and what most people mean when they say you have "high" arches). When you are wearing pointe shoes, it's especially important to keep the medial arch lifted and the lateral arch pressed down against the floor in opposition. This will prevent pronation which is where the wobble ultimately comes from. You can strengthen this arch by using a Theraband or towel and pointing and flexing your foot against it. But always - always - concentrate on lifting your arches when you are at the barre so you can count on them being there for you in the center.
By starting from the top and working your way down to your feet, you can minimize that feeling of wobble and maximize your control when you are in the center. Happy dancing!