1. Why is it important for blockchain networks to be high availability networks?
Because blockchain is a global network it has a daily use case. Millions of transactions are made daily and a blockchain needs to be up and running 24 hours a day, 7 days a week, 365 days a year to verify, and validate these transactions.
2. What is it that enables blockchain networks to have such high availability?
Incentives are what enables blockchain networks to have such high availability. Through mining you are given rewards. If there are less miners, the difficulty to mine becomes easier making it more appealing for more miners to jump in which then makes it harder to mine.