Ok since Battletech is essentially ww1 and ww2 in space
Not really. The maneuvers of ships that can accelerate for days and fighters that accelerate for hours don't favor broadside battles and sustained fighter dogfights. See High Speed Closing Engagements in Strategic Operations for the some of the potential oddities of BT space combat.
why don't battletech warships have main and secondary battery turrets like ships from those eras?
They do have turret-mounted weapons, which is why weapons have firing arcs rather than firing in fixed lines. However, those turrets and their descriptions are left to fluff while the weapons in game play are handled by the simplification of firing arcs. Mounting dozens or hundreds of weapons on explicitly-defined, individually targeted and targetable turrets in the fashion of ground vehicles also gets messy from both conceptual and rules approaches. The multi-turret system eventually developed for support vehicles was burdensome enough.