Raising money is ok. Selling 50% of your company for 10B the company when apparantly you have trillion dollar defensible business dont any business sense.
You need money to turn it into a trillion dollar business... Selling equity is how you raise that money.
If you were sure it will be a $1T business you have more reason to sell equity and accelerate the growth of your company, because you know the remaining 50% is going to be so valuable.
What would they have done instead? They still need to fund the operation somehow, and raising money is a good way to build partnerships.