Why open source it?
Just another virtue signal while their real motivation is something more sinister?
They are a for-profit publicly owned company.
Are investors happy about spending billions to open-source it?
a, they're not really open sourcing it, they're releasing it under a license that says you can use it for what they say. So it's marketing mostly, both external and internal to try and appease the "AI ethics" crowd. And honestly, b, their strategy is incoherent anyway. It's a tech company with too much money and no acute market pressure hoping to find something that sticks.
Traditionally a company with too much money returns it to the shareholders as dividends, but that seems to be passé...
Probably partially to reduce momentum in profit extraction from competitors
I wouldn't expect the open source licensing terms to be particularly permissive, and it might even be personal-use-only. In the end it might look more like source available than open source.
I think their investors should be happy about it. Once more open source models are released, a lot of ai companies will be freed to focus on other things, thus increasing the overall economy.