First of all because running a node can be difficult 
There's a few things that make developing on your own node connected to the network particularly annoying.
There are even more issues you can face with Nodes, so that’s why you need a node provider.
Node providers are essentially teams that offer access to Nodes without having to run your own node. So instead of sending your requests to a local node, you can send them over the internet to a provider offering an identical API that is running fully-synced, up-to-date nodes available 24/7.
As we like to say: keep calm and use GetBlock https://getblock.io/
There's a few things that make developing on your own node connected to the network particularly annoying.
- It can take a lot of time to set up a node - up to weeks! The bane of any developer is spending a lot of time setting up for a tool that doesn't directly contribute to what they're trying to build, and nodes are among the worst offenders.
- Nodes have to be managed: Nodes regularly need to be upgraded every few weeks, and occasionally re-built from scratch. Individual nodes can fall behind the network for various reasons.
- If we’re speaking about a single node, it’s fine and dandy especially when you're building a personal project. But what happens when you can't make your node server large enough to keep up with the requests you're sending it?
There are even more issues you can face with Nodes, so that’s why you need a node provider.
Node providers are essentially teams that offer access to Nodes without having to run your own node. So instead of sending your requests to a local node, you can send them over the internet to a provider offering an identical API that is running fully-synced, up-to-date nodes available 24/7.
As we like to say: keep calm and use GetBlock https://getblock.io/