Could someone please explain....

So I do not understand why there can't be a standardized baby clothing scale, I get so confused with every brand having a different way of sizing everything,  So Landon is roughly probably 14ish lbs now and he is almost 4 months old, but adjusted age of 2 months.  So while he fits in some 0-3 because it fits larger such as Circo from Target, but is in some 6 month when it is Carters????WHAT THE WHAT!! Why can't it be a standard thing.  Everything should either be 0-3, 3-6, or they should stick with 3,6 etc. Or just plain put the weight range.  I mean everything else baby is confusing enough why should clothes be too.  So now my 4 month/2 month old baby is wearing a 6 month old pair of pants because its from carters...I'm just saying...