Why did CW's Arrow create new characters with traits from established comic book characters instead of just adapting them properly?

Thea is literally named Thea "Dearden" Queen, they made Sara Lance the new Canary even though Laurel (the real Black Canary) was in the series, and they created a new son for Oliver with the same plot as Connor Hawke instead of just adapting him properly?? Even Mia Smoak seems to have characteristics of Olivia Queen from Kingdom Come.

I know the series ended a while ago, but to this day I don't understand the difficulty in adapting the characters correctly instead of creating new ones.