Legos have typically sold more to boys. For a long time, Legos were meant to be gender neutral, but it didn’t work out and 90% of Legos sold were to boys. It was bad enough that Lego felt a need to create girl targetted legos in 2012, to try to capture some of that market. The “Friends” Lego sets were enormously successful, and tripled sales of Legos to girls in the first year it came out.
It’s also common to target an audience by having the characters be reflective of the audience. If you write a book targeted at elementary school boys, you usually want it to start an elementary school boy.
So I’m not surprised that most traditional LEGO figures are boys after decades of boy dominated sales.