Why do we need distributed Systems?

There are two main motivations for this:

• To scale beyond a single machine — storing and processing data in multiple nodes.
• To increase availability — ensuring a database isn’t a single point of failure.

These two goals are closely related. In general, scaling a system by increasing the number of machines negatively affects availability, since the probability of encountering failures increases statistically. Thus, achieving high availability is almost a prerequisite to scalability.

https://medium.com/@jeeyoungk/why-i-love-databases-1d4cc433685f