It's quite simple. xAI bought a shit ton of GPUs for Grok thinking they would be competitive. When that didn't pan out they found themselves with either giving away Grok for mostly free or renting out the capacity to someone else for a shit ton of money. They chose a shit ton of money.
Alphabet owns some SpaceX shares, which makes Google's sudden 90-day compute contract with xAI seem a little less than coincidental