It was the same on the -200 and then was carried over.
If ATC asked you to reduce to 180 then flaps 2 was a reasonable configuration, but I don't think it was used as a take off setting, although I stand to be corrected on that, and it didn't really help on approach as if you were flap one at 190 then you could select all the way through to five and go for 170.
In much the same way flap 10 (160) wasn't often used. All of this was before the rudder-over problems when all the flap speeds were increased.