If I remember correctly, this came up back in 2017/18 when Starfinder was still new. I don't have any links handy or anything, but I seem to recall the main point being that spellcasters in 3.5/PF1E are seen as mechanically 'too powerful,' at mid-to-high levels. Why have a fighter with a sword when you can just throw out fireballs all day - that old chestnut.
They accomplished this re-balancing by toning down spells (every spellcasting class has lower spell progression than PF1's 'dedicated' spellcasters, as well as squishing level 7, 8, and 9 spells down) as well as making 'martial' damage tied to weapons that scale to higher damage dice by level. In space, the fighter doesn't just keep using the same 1d8 dmg Longsword their whole career.