How so? Three Kingdoms was a huge success and Warhammer II is ridiculously popular with a very positive community and great DLC/FLC. Arguably Rome 2 and Atilla weren't as great but they seem to have really turned it around in the last 3 years. Before that Shogun 2 and FOTS were also great games.
I agree with you that Shogun and 3K were good additions
Personally I just hate how much wasted potential exists with the series, after Napoleon most players (me included) just wanted that layer of polish with Empires scale and possibilities. Sega and CA certainly have the ability and resources to make that happen.
Instead we got that whole Rome 2 mess and milking the players with DLC (not talking about FoTS, more blood DLC and factions that should have been in the game at launch) and reused assets for Attila etc. Then SEGA brought the warhammer licence and focussed on fantasy titles in a series that is about history.
I can understand fantasy fans happy about that (I like 40k myself), but it should be it's separate IP away from TW with its own separate team.