Because the mantra itself relates to the Sun Square. That was the reason for saying or focusing on "the energies of the Sun Square", because this is different, although related, to other solar magic.
Each mantra within "AUM HRAAM HRIM HRAUM SAU SURYAE NAMA" has its own unique energy, with words like aum and nama not being necessarily solar related. All of this is different from if you just chanted "Raum" or if you breathed in energy from the Sun.
Visually, this can be seen differently than if you were just chanting and visualizing the Sowilo rune, as another example, despite both being solar related. Since higher level magic like the Sun Square can be sensitive to its specific parameters, that is why I focus on it exactly as it is, not just broadly as solar energy.