Earlier quoted context omitted.
25 mm became Vogue and cycling because wind tunnel testing showed it was superior in aerodynamics combined with a new carbon clincher rims If I recall correctly
My daily ride is an old race bike so 25mm is the widest that will fit between the chainstays. Also the widest that would not bulge out on old Mavic Ksyrium rims. If not for these questionable life choices I'd be on 30s. According to Continental, 28mm is the prevalent width for TDF teams.
25mm was the older "skinnier" size that was prevalent in the peloton, or even 23s or smaller.
I think it also became apparent that rolling resistance was reduced on wider tires, so if an aerodynamic (and weight) formula could be made to make 28mm viable, it was better.