If you played without offsides then you would have strikers just camped out at each goal with defenders draped on them. The midfield would be just wide open long kicks back and forth. It would look like total chaos and once teams and coaches adjusted to the rule change scoring wouldn’t change much either.
ETA: Hockey has close to the same rule as soccer. Illegal formation penalties in football and three second violations in basketball are sort of in the ballpark. Infield fly rule in baseball too. All these rules are there to equalize each side so that there’s not an unfair advantage.