You can save money and get higher uptime. Without it using a cheap provider for open models would be risky because they might go down a lot, but routers can detect that and instantly switch to a different provider. They basically take away all your exposure.

The other thing is convenience and centralized security from using one gateway to access everything. It's a lot better than having to deal with N accounts with separate limits and monitoring. And giving your payment details to one company instead of 20 is obviously safer.

Investors like them because the pricing is inherently usage based so there's zero risk of clients using more tokens than what they paid for. Guaranteed profit as long as they can keep a modest amount of customers.