one plus point is their developer community so If you want a platform that has a strong developer community, then you go for Ethereum. Also its decentralized so security is another plus point. Also almost all Defi projects are built using Ethereum which is a huge plus point for this platform. Taking about other platforms i think stellar, cardano and Rsk will be its worthy competitors
ETH is not a decentralized project, but it is a semi-centralized project. Personally I think the reason why ETH is more popular than other smart contract platforms due to ETH itself as the silver of cryptocurrency. When you are using their platform, the most basic thing that you need to know is the stability of the project and the demand. Let's talk about Waves, for example, it is a good and easier platform to make a smart contract but why there is so little people use their platform to make a smart contract? it is because of the demand for the project, the demand for the project is the most important thing because it affects the network and the value of the coin. ETH is well-known in the world compared to the rest and the majority of people know how to use it.