The way it's set up now, it allows you to switch to a specific power quickly without changing what you have equipped.
Example:
You want to Freeze a group of Zin and then smash them with stomp.
Throw your Freeze Blast, press F3, Stomp, press F1, you're back to Blast.
In your example, when you press F1 to go back to Blast, you'd change it from Freeze to Fire, and you may not want to do that.
However, that does not make your request any less valid, just letting you know why it's set up the way it is now.