what exchange share sorderbook with bittrex?

I don't recall. The odd setup was explained back then by @clayop, a witness and member of Steemit Korean community.

in 2017 SBD was over $1.3 for at least 3 months going to $6 one day how didnt this break?

I don't understand what you mean by break. Different shocks have differing effects, depending on magnitude, system conditions, duration, etc. Even now SBD is slowly in the process of recovering: The peg-to-$1 price for STEEM has declined from 0.415 to 0.403. Unfortunately STEEM has continued to decline in price but unless it continues to decline to zero, eventually SBD will likely re-peg.

and if such an issue why dont witnesses use other SBD changing parameters as in the bias

Bias has undesired secondary effects including increasing the total Steem inflation rate. It isn't an effective tool.

namecoin is used to create websites with zeronet

OK, sounds cool. I haven't followed namecoin recently.

if you mined how did you use before?

I'm not sure if I understand this question. Maybe you were asking how I used namecoin? At the time the only way was the original (forked from bitcoin) command line tools and a proxy you could direct your DNS to make use of namecoin names.