Why is Riot so scared to nerf any core parts of Ahri?

{quoted}

Or if someone care to explain, what's the reason or context of this change?

It means what is says, so it has more counterplay. Now you can tristanna jump away and it wont cancel it mid jump if the charm lands on you . wont stop a lee sin Qing to your face, ETC. weather its a big nerf or small (depending who you are fighting i assume?) it is still a nerf.