Probably not a infrastructure capacity issue but a limited amount of cryptocurrency in a hot wallet for transactions.

Cold wallets don't scale, and that's the entire point of them.

"Hot Wallets" can be hacked, because they're connected to the whole system. "Cold Wallets" are offline, and require human intervention to transfer money into and/or out of.

Figuring how much money to keep in the "Hot Wallet" is a tradeoff in services, convenience, and security.

Can't tell if you're trolling or not... ;p

That works, so long as you've refactored your infra to the point that the computational resources (whether server nodes or hard disks or or database shards) are modular enough that you can just add more stuff and it will play nice with everything else. That objective -- not a cute UI that lets you change one of the numbers -- is the hard part.

And yes, it is to Coinbase's discredit that they haven't done so, but (assuming you're not joking), they could very well not be at that stage. It's typical for startups to have technical debt like that.