If it hasn't happened already, someday a team member will give you notice, and the reason will be more money. Sometimes, that's even true.
Most of the time, though, that's code for "I don't want to get into all the reasons I'm leaving, or to have you try to talk me out of it. So I'm going to say they'll pay me more than you will."
There are all kinds of studies that put money fourth or fifth on the list of reasons why people like their jobs. First is usually feeling needed and valued. Social connections are important too, as is a friendly, safe environment, and feeling like you're doing good in the world. When your team member says it's money, chances are it's at least one of those other things.
By the time you're having the conversation, it's probably too late to keep that person. But do a good exit interview, asking about all those other things. You'll get some negative feedback; those are things you'd better fix if you want to keep the rest of your team.