i believe mappers use ar to control the amount of visible objects on the field, a slow map with a high ar is going to look bad because there aren't as many objects visually appearing at the same time and also gives the vibe that the map is fast.
a fast map with a low ar is going to look bad because there are too many objects visually appearing at the same time and so it confuses the player into thinking the map has a slow rhythm/flow, and also looks very clustered/messy.
You won't see many low ar maps in the map pool simply because a good mapper will always pick the ar that makes their map looks best in. ar10 is generally used for maps that have high flow speeds i.e. image -material-, big black whereas ar9 is "not too fast" but also "not too slow" for moderate/high bpm maps. maps that are ar8 and below tend to be maps that are easily dt-able; the map is going to be at a relatively low bpm ~160 with pretty low spacing and sv which doesn't meet the difficulty requirements to be an owc map (unless in dt bracket), or maps that have a very low amount of hit objects.
Personally i don't enjoy hitting a circle and then looking at my background waiting for the next one to pop up, but i also don't like to focus on so many objects appearing at once creating confusion, and my playfield looking incredibly messy too.
tl;dr version: mappers pick ar depending on the speed of the flow of the map, and to not make their map look empty or clustered which is why not many ar8 and below maps are picked because they are generally easy and do not meet difficulty requirements
a fast map with a low ar is going to look bad because there are too many objects visually appearing at the same time and so it confuses the player into thinking the map has a slow rhythm/flow, and also looks very clustered/messy.
You won't see many low ar maps in the map pool simply because a good mapper will always pick the ar that makes their map looks best in. ar10 is generally used for maps that have high flow speeds i.e. image -material-, big black whereas ar9 is "not too fast" but also "not too slow" for moderate/high bpm maps. maps that are ar8 and below tend to be maps that are easily dt-able; the map is going to be at a relatively low bpm ~160 with pretty low spacing and sv which doesn't meet the difficulty requirements to be an owc map (unless in dt bracket), or maps that have a very low amount of hit objects.
Personally i don't enjoy hitting a circle and then looking at my background waiting for the next one to pop up, but i also don't like to focus on so many objects appearing at once creating confusion, and my playfield looking incredibly messy too.
tl;dr version: mappers pick ar depending on the speed of the flow of the map, and to not make their map look empty or clustered which is why not many ar8 and below maps are picked because they are generally easy and do not meet difficulty requirements