why does the art style kinda look different like their eyes are bigger and their faces are...

Well bwt art have changed significantly over the years... the earlier manhwas used to have longer shaper faces with sharp , thicker outline and much solid coloured background...but in past 2-3 years the art become more refined , the outline became thinner and sharper , their faces became much rounded , and the background became much brighter and sparkly... so yeah whatever change you noticed is absolutely correct... it's the same artist trying to improve their art...