It is really important to have a high availability network because it must be available when I and other people need to access it. 24/7 .365 days a year so it is possible to do transactions at any time from any place you can connect to the internet.
What enables blockchain networks to have such high availability is greed. The blockchain miners or exchanges are paid to keep the networks running smoothly. It is the transaction charges that they receive that makes it worthwhile for them to ensure that the blockchain is always available.