Imo, Ichiran is popular abroad cuz 1st it's introvert friendly this concept is unique to most of us 2nd you can customise your ramen like noddles, broth consistency , toppings etc etc . Thats all i can think of as of now
Me and my cousins visited to one of these restaurants exactly last year’s trip to Tokyo. The experience was amazing for the first time we entered! And the ramen came out pretty nice too!
The ramen at Ichiran is really good. If I recall correctly, a full portion refill of noodle was 150 yen in 2014. Ono, have you also tried 麵創房無敵家 at 池袋? I heard that this one is really good too.