Maxperson
Morkus from Orkus
Rolling is a default method and 57%(slight upward rounding) of PCs who roll will have a 16 to add the +2 ASI to. WotC doesn't have a goal to prevent 18's in the primary at 1st level, or even 20's, since rolling yields those as well. If they wanted to prevent 18+ at first level, rolling would go away or change to d4's or something.I believe that it is to prevent PCs having an 18 in primary at 1st level.