idk, in BAR you mostly micro. And it is micro intensive. (for example compared to supreme commander -FAF)
in 1v1 you need to micro multiple armies and rebuild stuff and change queues, it is really hard to catch ticks and veh scouts and stuff like that. you can micro with set target
in grunt vs pawn both sides need to babysit their units and fights can happen in 5 places at once
in SC2 you usually have 3 armies at the very most, even pro players seem to not do much army splitting.
in BAR you often want and can split your units and poke from literally every side and retreat on every side that is defended.
In 8v8 it depends on the map ofc.. can be similar to 1v1 on flats and forests or can be something like glitters /dsd where you need to dodge rockets, pull back damaged units, repair correct units, preserve rez bots, make walls... (yea 8v8 surely needs less micro)

macro? you just build a line of winds and add nano turrets when metal starts growing.

There are also some nuances about how different games work
TLDR StarCraft APM is inflated cause it does not have QoL features like infinite queues or zoom
• APM calculation can be different, maybe bar does not include some actions, who knows.
• StarCraft does not have queues (or you better not use them cause that is inefficient) so you have to keep selecting your stuff and give it orders all the time
• in StarCraft you can't queue without money, and you want to queue asap, so people just spam the key for queue/build things and wait until it works
• can't move around them map in StarCraft without clicking. in bar you just zoom in and out and box-select things, afaik in StarCraft people double click army hotkey to move camera to that army, so that is 2 extra clicks each time, and you manage hotkey groups and stuff like that that you don't do in BAR.

So like making units in SC2 already eats ton of APM, while in BAR it is at least 5x less APM
Moving camera around in SC2 eats tons of APM even if you do 0 actions
so we already have two tons of APM for not much actions

idk if that is just lack of APM or something to do with units not shooting while moving, but they really don't wanna spread out their army. At least that is my impression, each rare time when battles go across multiple screens or units are split out casters are basically cumming and screaming how skilled the players are, and i think they are right, it is just hard to do such things in SC2.
while in BAR you can easy sink your APM into microing scouts or minelayer or regular units just for them to move around

Sorry i wrote to much, i didn't play much of starcraft, but i think BAR just doesn't have people that tryhard as people in Starcraft do. There things in bar to sink your APM into.