In another words you said: "This is unique, but idk why" 
And? Java is old well know language. They didnt invented Java as like as this made Vitalik and Gavin Wood (Solidity for Ethereum).
And? Java is old well know language. They didnt invented Java as like as this made Vitalik and Gavin Wood (Solidity for Ethereum).
Why java
They chose Java because it's a popular language with huge community and reliable networking libraries which is critical for 100 validators being communicating with each other all the time.
If you check the history of commits, you'll see that large part of codebase has been developed by community members. semuxgo started this project back in 2017 and on mainnet launch in 2018 many other Java developers and blockchain enthusiasts joined the project: cryptokat, orogvany, witoldsz, phash, honeycrypto, mdodong.
Why semux is unique
- as mentioned above, semux is not a fork and its codebase written from scratch. So it's literally genuine software.
- they developed own modification of BFT consensus [1] which makes Semux faster than competitors like Ethereum: 15 tps vs 166 tps semux
- semux is censorship-resistant, 2/3 of validators is enough to keep the network live. Imagine if due to escalation of China-USA trade war [2] one of these countries will decide to isolate the internet completely. For coins like Bitcoin or Ethereum this will be a disaster, there will be no transactions in weeks or months due to high difficulty and low hashrate. But Semux will continue working with no issues (unless there is no more than 33% validators in China, but this is not the case - see the map [3]
- high passive income, at the moment 36% yearly yield; one of the highest in crypto industry
- according to semux roadmap [4], the project features not only Semux BFT consensus, but also Virtual Machine and On-Chain governance. So Semux took the strongest features of Bitcoin + Ethereum + Tezos and added more on top.
- No ICO, no IEO, no crowdfunding - in 2019 when every project seeks for our money, this already sounds extraordinary
- Semux is one of few projects driven by international community, so there is no force in the world which can shut it down like centralised projects baked by corporations (EOS, TRON, ETH, and almost all the other cryptos except Bitcoin).
[1] https://github.com/semuxproject/semux-core/blob/master/docs/Semux-BFT-Consensus.md#semux-bft-specifications
[2] https://en.wikipedia.org/wiki/China%E2%80%93United_States_trade_war
[3] https://semux.info/delegates
[4] https://www.semux.org/#roadmap