Their stock just took a 20% dive because their main cash flow engine up to this point, the FB app, is showing stagnating engagement. Unless they want to take even great stock hits, which would lead to: greater difficulty to hire, greater difficulty to finance, more employee turnover, decreased ability to fight government regulation, et cetera, then they can't let this investment be wasted.

The acquisition price is a sunk cost. They still have the asset, and I agree its important for them to not waste it.

Sure, but it is analogous to what investors are valuing it with regards to their stock for.

Zuck paid $19 billion for it and needs some form of return on that investment? You can't just lose $16,000,000,000 in personal wealth in a day and come up with a plan that maxes out at ~$1 billion a year in revenue.

Better something than nothing?

A bonus is to combat competition like Snapchat to Instagram by having a solid alternative.