That would make things too easy
Although recently a fan-made graphical update for EoSD (TH06) includes the option of having a visible hit box. In fact (TH06) is the only game in the Touhou series that didn't have a hit box being visible at all. In the later games after TH06, when you used focused fire, you would see the hitbox on your character.
Example - in this video if you pay close attention to the character being used and utilizes focus fire, you can see the hitbox being displayed.
Regardless, even if you were to have the hitbox displayed constantly, that doesn't stop the games having an, imo, "enjoyable difficulty" throughout the game. It's emphasized that you graze the enemy's bullets and attacks. You also earn more points when you dodge and graze the bullets without using the hitbox display.
There are some times where in fact the main goal of certain attack is that you must outlast the timer of the spell card and simply survive it till it runs down.