The hot wallet is a minuscule amount of the total number of 371k.

Coinbase has to constantly source new coins from miners.

Follow the incentives the exchange going down for maintenance always seems to come at a time that’s most beneficial for them.

I don’t believe that they can’t handle or anticipate the capacity.

That said I’m not proclaiming to have special knowledge. This is just my hunch, based on years of observation.