honestly i think it's as simple as people like numbers that end in 0 or 5. 40 60 80 100 is easer to say, to see, to remember, and to hear, than 43 56 72 101. Also when sending specs to manufacturers making them it's easier for them to decipher. SO EASE OF USE
well, that can be true, but also not true if you look at what guitar sets offer, and they are all odd and different, but people only look at the first and last gauge (FE: 10-46, 09-42)
custom and endorsed sets usually have a lot of specific numbers, lighter G and D string, heavier E ecc.
only bass sets, if I don't remember wrong, started with "even" sets due to Ernie Ball, because Fender sets were odd, Rotosound RS66LD in the 60's mentioned the exact gauges (48-63-82-102), then switched to "written 45-105", but still makes them with those gauges,
their Jazz77 also are like this: the 45-105 set has 50-70 as G and D, and the 50-110 set has 55-75 G and D.
La Bella uses a lot of odd sets, but also have the "even" sets.
IMHO "balanced sets" are not usually that balanced, and I still prefer odd sets, for example I like heavier G (Rotosound RS66LD, GHS P-flats 55-105) and lighter E strings, because the finger's arc and position prefer to have lighter strings far away and lighter strings nearby.