Why is 1” throttle so uncommon

Mini Bike & Go-Kart Parts

I just recently got my first mini bike frame as a build project. I’m almost done all I need is a twist grip throttle and a brake and I’m ready to ride. I ordered a twist throttle off Amazon and it’s just under the size I need for the handle bars I have. It’s a 7/8”(22mm) where I need 1”(25mm). I have been looking everywhere for a kit like the ones on Amazon but everything is 7/8” not 1”.. why is this?? I would think that it would be just as easy to find 1” as it is to find 7/8”. The frame I have does look older, but it still shouldn’t be that hard to find a throttle for this bike. Can anyone who has 1” handle bars for their mini help me?