shouldn't 소는 이쪽으로 와요 also work?
As well as 소가 이쪽으로 옵니다.
Nobody but an announcer would talk this.
Is it also correct to say, "A cow comes this direction"? April 15, 2020.
Why is it 소는 and not 소가?
Pretty sure you can use both. To rule out one you'd need more context to see which is more applicable.
Why cant i use 이쪽에 rather than 이쪽으로?
~에 is more for destination, eg "at the x..." while 으로 is for direction, movement, eg "(going) that way, (going) to school". I think 이/그/저쪽 always uses 으로 as the word always implies a direction, a movement somewhere, instead of a static location.