This is because it shows a lack of care, and disrespect for other members reading the thread.
I blame movies.
Knew-New
Knew is past form of know and new is something which has been done for the first time.
Then-Than
Then means kind of times and than is used in comparison.
Their-There
Their is possessive form of they and there refers to a place actually.
Even-Eventually
Even generally refers to mention something specially. But eventually refers "in the end".
To be honest I made lots mistakes. It is not that I don't know difference between words, I blame my language, as we write like we speak and it is very easy to misspell something (these examples are some of my mistakes):
"They" -
"day""know" -
"no" or sometimes "
"now"".
"Too" -
"two" or
"to" (not necessary in that order).
"Than" -
"then""won't" -
"want""on" -
"in""literary" - "
literally"
"yes" -
"no" - not really

You will find lots of my posts edited because of this, even days after posted. Many remain unedited.
Other then this, I always see red lines under words if I didn't spell them correctly

I don't really want to talk about my grammar