Polygon enables Ethereum to connect to other blockchains and the aim of the protocol is to "help" Ethereum in scaling while supporting its core functionality. It does not try to take network participants from Ethereum, rather it creates a symbiotic relationship. Although Polygon is a separate blockchain, it connects to Ethereum as a "side chain". This means that Polygon's blockchain will run in parallel and it can communicate with Ethereum if needed.
Developers of so-called dApps (decentralized applications) who want to distribute an Ethereum-dependent application, but also want to avoid its expensive fees and network congestion, can instead develop everything on Polygon. In other words, dApps built on top of Polygon can interact seamlessly with those built on Ethereum.