Why is only the ? and ! put at the front and upside down of a sentence in Spanish?

https://yiffit.net/post/8361682

Why is only the ? and ! put at the front and upside down of a sentence in Spanish? - Yiffit.net

Why not periods? Why doesn’t every sentence in Spanish that isn’t a question or exclamation start with a period floating in the sky?

I would assume it's because it leads the reader to what tone to use in a given sentence. The question mark or exclamation point would be useful in tone throughout the whole sentence, but if neither is present in front of the sentence a regular reading tone could be assumed.

so why add a floating period when nothing being there allows for the same assumption and is much, much simpler and easier?

As a Spaniard: yes.
*si
*sí