Couple different reasons, I think.

The main one being that symbols and sounds control reality. Not really going to go into sounds or the power of the spoken word for this one.

https://californiafreemason.org/wp-content/uploads/sites/12/2019/04/MOC-063_CFM_Mar_Apr18_M02.pdf

The core concept of sacred geometry is that geometric order (shapes, curves, and constructs) precedes all physical existence – that geometry was invented by the Great Architect of the Universe as a structure through which to order all of creation. Under this tradition, its symbols take on metaphysical and symbolic meanings. “Geometry, or Masonry, originally synonymous terms, is of a divine and moral nature,” wrote William Preston, a seminal figure in 18th century British Freemasonry. “The contemplation of this science in a moral and comprehensive view, fills the mind with rapture… [and] proves the existence of a first cause.”

This is why they use these symbols in everything.

I think the other reason is its a club, only the ones who know are even aware they have meaning.

I do like the mystic masonry books explanation that they are messages intended for those who are aware enough to receive it.

The Traditions and Symbols of Masonry do not derive their real value from historical data, but from the universal and eternal truths which they embody.

In this book it is not attempted to explain all of the symbols of Freemasonry, or to completely un fold the philosophy of the Secret Doctrine. Such an undertaking would transcend both the time and ability of the author. The aim is rather to show a few points of contact, to outline methods of interpretation, to convince the unbiased reader that in the ancient mysteries lies a mine of wisdom far beyond all modern achievement, and to invite the co-operation of Masons in upholding these Ancient Truths.

It is in the ancient symbols of Freemasonry that its real secrets lie concealed, and these are as densely veiled to the Mason as to any other, unless he has studied the science of symbolism in general , and masonic symbols in particular. In place of the term Mystic Masonry, the term Symbolic Masonry might have been used alone, but just here lies the whole secret , a profound mystery, and few Masons up to the present time have had the interest or the patience necessary to such investigation. This is a fact, and not intended as either a criticism or a reproach . If lacking a knowledge of the profound meaning of masonic symbolism, and its transcendent interest and importance, Masons have allowed the whole organization not only to fail in all real progress, but to degenerate, that is indeed a reproach.