There are a lot of reasons someone would not want to play on your server. Many players will just walk around and then leave and you always wonder why. I used to wonder this too until I found out why. We will go over the main reasons why you are not getting players in your server like Builds, Configurations, Player Base, Player confusion etc.
Builds
Most of the time you always see players just join look around then leave. Usually this is because the builds are recognizable from other servers if you have Non-Exclusive builds. Also, it could be that the builds you have are not eye appealing and look like every other server in existence. So, I would recommend if you have the money get a build team. You can go on MC-Market and find yourself build teams like Senior team, McSetups etc. It will cost a bit but will help with getting players on the server!
Configurations
The looks of your configurations are crucial to a successful server. Anything visual to a player must be done correctly. Also, Economy stuff must be balanced, or players will quit due to unfair advantage. Things like GUIs, lore’s for items, and the layout of everything matters. If it does not look good at all players will leave.
Player base
If a player see’s that your server does not have many players on and interacting with them, they will most likely leave. A way to help with this is to be online as much as you can in the start interacting with your community and building a community by talking to new players in chat. Getting them to join a Discord will also help with building a community because they will be more likely to stay if you can get them hooked in the discord.
Player Confusion
Let’s say a player joins your server, they look around and they really don’t know what to do. That is a bad thing, we really do not want something like that to happen. Make sure everything is clear to other players. Have a friend join the server and do not tell them what to do at all and see how far they get. That is the best way to do it. Once you have figured out what causes confusion you can fix it and more players will stay!
Ideas
I would hate to say it, but your idea may be too bland, to unoriginal. You need to refrain from copying other servers and make up your own ideas. Even if it requires a custom plugin, no worries. This will help increase your players a lot if you have really good ideas and you put them into place in your server.
Conclusion
I would recommend evaluating your server and looking for some of these flaws. Also, I recommend asking people who are on your server for some input on what they would want. But if an idea seems to off/outlandish I would recommend to not do it.