Because what we really need is more games about men in chainmail with spears fighting each other in Europe.
Seethe and cope but your historical games are boring. They are all exactly the same, with the same factions, the same units, and the same gameplay. Warhammer Total War breathed life back into the series.
Before, every army was composed the exact same and the only differences were which factions had slightly better cavalry or infantry or archers. In Medieval they are literally identical in Europe. In Warhammer you have armies of skeletons, and vampires, armies of rat-men with machine guns, giant demonic monsters, and dragons, griffon riding heroes, and earth shattering magic to change the entire battle. Oh, and you still have boring old men with spears if you miss them that badly.
It's just fundamentally more interesting and fun to have epic battles between supernatural heroes than watch brown men with grey spears spend 20 minutes slowly poking at each other until they flee at 50% losses.