Let me explain why.
The word people mean to say is Regardless. We have the word 'regard' + the suffix 'less'. The suffix 'less' is used when one wants to indicate 'without'. So Regardless means 'without regard'. Synonyms would be 'anyway', 'nevertheless', and 'despite everything'.
Regardless of the threat, Jon Snow still tried to save the Free Folk from the evil that lurked in the North.
Let's analyze the improperly used 'word' Irregardless. It has a prefix "IR", which is negative in meaning. It means 'not'. So with what we already know, Irregardless means 'not showing no regard'. Now does that really makes any sense? What we have here is a double negative. It basically means showing regard, which in the end means the total opposite of what was meant.
Irregardless should never be used. It is wrong and must be destroyed. Hopefully this blog post gets us one step closer.