It's not primitive, believe me... It might rather be because no one else makes such complex searches possible (perhaps with the exception of ITA).
Take an example: From anywhere in Germany to anywhere on the Mediterranean coast, next summer, max. 1 connection, for 5-8 days, return to same airport: https://azair.me/!4gDR ... is generated in 2.3 sec. That's not long
Or what did you mean by complex searches?