Why there often an additional filler word in Indonesian language?

Why do Indonesians always add a meaningless filler word at the end of the sentence?

For example:

• “ini apa sih?” instead of “ini apa?”
• “ga gitu njir” instead of “ga gitu”
• “itu apa deh?” instead of “itu apa?”
• “mau minta tolong dong” instaed of “mau minta tolong”
• “ga boleh gitu wkwk” instead of “ga boleh gitu”

The answer is that Indonesian use those words to soften their words and to make sure it doesn’t sound offensive or rude. It also helps the sentence to sound less harsh. “Sih” could be equal to English’s “though,” like “Not like that though.”

In linguistics, this is called modal particles.