Why do tv hosts like Steve Harvey or Ellen degeneres read off giant placards instead of doing their own thing?

They're liberal talentless hacks.

I doubt if it would be better.I could see a host going off script for a bit and makeing the show better.I wouldn't believe they could do a whole show good on their own

OR even use a ear piece, I guess they are so old they have a memory loss..

Some hosts are dumb and stupid because they are rich idiots who need to read a script.  

All hosts read off cue cards 

Apparently Ellen gets mean when she is not reading a prepared script.   No one knows about Steve though as people are not allowed to ask him questions or make eye contract.   

The rest of the stage crew is looking for a verbal prompts to do what they do. They aren't reading every word they say off the cue cards, but when specific transitions need to be prompted the crew is listening for those keywords.

There is not a talk show host ON EARTH who isn't mostly scripted. Yes it's obvious. 

Do you actually think comedians come on stage and just make up their jokes on the spot?