WZ has learned from sources inside WWE that the reason The Undertaker, Bret Hart and other big name legends weren't used on Raw last night was because Stone Cold Steve Austin and Shawn Michaels weren't available.
As reported, Austin and HBK were both in Las Vegas for a hunting convention which is why they weren't in Houston for RAW.
Because those two could not make it, WWE decided to drop any plans of using other big name legends, most notably The Undertaker and Bret Hart. The feeling was they didn't want to have a bunch of legendary names on RAW and it draw attention or heat on Austin and Michaels for not being there.
Mick Foley was there obviously for the Hall of Fame announcement.
As for Ric Flair being there, his appearance was justified as he was on RAW a few weeks ago and is slowly being worked back in as a regular role player on WWE programming.