Some players want to share their big wins while some want to remain silent but as you are aware about the username only your position is not at risk completely and you can do it.But still it's our own preferences and casino needs it as advertising promotion to attract new players.
Sharing it will help you to record your win. It will be saved on the Internet after your sharing. If you don't share, and don't save any screenshot on your devices, you will never be able to find your past wins in future.
In addition, your adrenaline should be high when you get an amazing big win and it is hard to control your intention to share it around.
If talking about big wins then yes there must be similar big wins before also on Rollbit like the NFT lootboxes giving away million dollars BAYC and punks.
Rollbot NFTs have different use cases than BAYC NFTs so I don't think it is a good comparison here.