The userlist from is a GET post. That means all the form variables turn into URL variables. The reason for this is it allows linking to a pre-filtered userlist.
What you're seeing is just the form variables displaying as they should. This has not changed between CB 1.x and CB 2.x. This will only happen when a search is actually made. For proof of this see our CB 1.x demo site below.
demotemplate.cbdemosites.com/index.php/users
Click Search Users, type some characters into username, press enter. You'll notice the URL has the same type of variables that CB 2.x has.
Your screenshots are misleading to this, because your CB 1.x userlist screenshot doesn't have a search made.
This behavior can not be changed. Your URLs can still have SEF, but those variables are not going to be SEF as there is no SEF rules for them (there can't be, they're not static variables so there's no way to reverse them).