I don't have any source and I'm not even Japanese, just Chinese so forgive my ignorance, but I definitely read somewhere that seppuku is actually relatively new to Japanese culture. It was basically constructed as propaganda for WWII era Japan and it worked in getting soldiers who romanticized the Sengoku era to follow this new Bushido code to always die in honor of their country. I can bet a bunch of people here aren't willing to ctb for that reason in fact a lot of us seem to want to do it in spite of our country and not to honor it.
Even if it is a real ancient tradition, then what does that mean? Is it really better for your country to suddenly embrace suicide only in cases where people are deemed unfit to live by society? It's already kind of like this in modern Japan which is why their suicide rates are so high. Many parents there are actually less likely to grieve (or at least show grief) for their dead children if they felt it was necessary for them to ctb. What we have now in some western countries isn't exactly ideal but personally I think it's better than society actively encouraging your ctb not out of concern or respect for your choices, but because they just don't want you around anymore.
Then again, maybe if that did happen, the methods would become more available and could even be further advanced upon to be near-perfect. In fact, I've said this before but theoretically if you really want to uproot society and convince everyone to embrace suicide as a choice people should be allowed to make, you have to start appealing to their selfishness. Right now people are selfishly trying to make themselves feel better by thinking they've saved lives just for talking down people who want to commit suicide and that's the main reason why so many are pro-life. Well I say, be the change you want to see. Make it so the majority of people also want to die/want you to die. Society is pretty shitty now but it could still be oh so much worse. If you're serious about wanting society to allow you to ctb, you have to make it so more people would want it for themselves.