Microsoft published Jet Set Radio Future, Panzer Dragoon Orta and Shenmue II (Xbox version). It's not like the previous games in those franchises were retail hits before coming to the Xbox. If anything, Microsoft kept those franchises alive longer. Jet Set Radio Future sold better than Jet Set Radio, Panzer Dragoon Orta sold better than Panzer Dragoon Saga and the Xbox version of Shenmue II sold better than the Dreamcast version.
Microsoft already killed two sega franchises by releasing sequels on xbox consoles: Jet Set Radio and Panzer Dragoon (and Shenmue didn't sell a lot on that machine too)
Xbox is for dumb people with bad taste
If you include the pack-in sales, Jet Set Radio Future and Sega GT 2002 were both million+ sellers on the Xbox. If anything, Sega should have capitalized on the renewed exposure that some of their franchises received on the Xbox and released sequels on both the X360 and PS3.