Add to that weak cell coverage, exorbitant fees, and a privacy nightmare of jumbled up offerings (Yahoo! Japan, PayPay, Line, Telecom, ISP services, etc.), and you get the full picture.
SoftBank is originally one of the big 3 telecom providers in Japan. We do joke around here about our phone bills increasing anytime Masayoshi Son makes a bad investment.
Too much money skews everything in product development
There's a reason why the iphone team was so small (https://www.theregister.com/2014/03/27/apple_employee_reveal...) you need to be ruthlessly focussed and not pressurised by outside investors or managers who don't know what they're talking about (Softbank)
I'm not sure what the money would be spent on at OpenAI. Maybe they will keep it small, and hyper-focussed. But I worked in VC for a while and VC money was described to me as rocket fuel, you don't want to go dousing it on things before the rocket is built because it stinks and has a tendency to blow things up