To get anywhere from east of Galway to anywhere west of Galway you need to cross one of four bridges in the city or go as far north as Cong which is in Mayo and about an hour away.
To get to one bridge you have to come through a reasonable amount of the city, to get to the other three you have to come right into the city centre.
The Corrib river widens into a lake not far north of Galway so there's limited options for where a new bridge can be and it'll still be nearer to the city than would be desirable.
Galway has lots of middle class jobs in industrial estates on one side of the river and lots of middle class housing in Knocknacara on the other. The schools are also disproportionately distributed towards one side of the river too.
It rains a lot in Galway so people are even more averse to cycling/walking than in other places.
Lots of roads are narrow with not much room for extra lanes or cycle lanes or bus lanes.
All of these things mean it's probably going to keep getting worse.