Never understand Winnebago (nor Jayco) model line changes, but it usuaully has to do with market repositioning. Sometimes a name disappears for a while and comes back on something completely different.
29B was never a MinnieWinnie/Sundancer, from introduction it was Minnie/Spirit, Winnebago's C entry lines, which were positioned to compete with Jayco midrange, F-R, FourWinds-Chateau-Dutchmen upscale lines.
Names change when Winnebago introduced a lower cost construction to compete in the entry price market, Minnie models went into the now upscale Outlook line, MinnieWinnie and Sundancer models disappeared.
Marketing reasons. Note also, at the same time F-R took the Sunseeker more upscale, Jayco dropped their entry Escapade, so they had different ideas about where the market was going.