Glasses provides a way to create a dual identity that does not feel forced, anything other disguise will have to make an extra effort which will feel forced.
Are glasses a good disguise ? Certainly not, but many will overlook that fact a Clark Kent and Superman have some resemblance, but totally different personalities, the only problem is - staff working at the Daily Planet see him everyday (like Lois, Jimmy, Perry) and it is more or less a matter of them knowing his identity but not saying it loud.