Situation A: Without gear swaps. Select your gear before battle, forcing you to weigh some stats or effects over others depending on the situation you plan on facing. This approach creates the need to strategize before battle, requiring you to weigh the pros and cons of your decisions and equipping only the gear you feel you really need for each encounter.
Situation B: With gear swaps. Carry around several sets of equipment that you can repeatedly swap in and out during battle for every move you do. You don't have to choose or strategize about what gear to equip over other gear for a battle because you're just going to use it all anyways. This completely removes the equipment strategy of an encounter in exchange for maxing out every needed stat for every move.
In short, equipment isn't meant to do everything, which is why every piece has pros and cons depending on the situation. If gear swapping is allowed it opens the ability to wear the best for every situation all the time and removes those pros and cons, which destroys the balance and cuts out the strategy that would normally be necessary when equipping gear. Strategy creates depth, being able to have everything all the time makes things stale.