When someone new joins, the first week decides whether they give you their best or just their hours.

Starting somewhere new, a person is reading everything for signals about whether they matter here. Being left to work it out alone is itself an answer, and once someone decides they are a set of hours, that is what you get. It is not a bad attitude, it is a reasonable reading of the information available. The window for setting it is short.

If someone joins your group, take the first day seriously. Learn their name properly, tell them one thing that is not on any list, give them something real to do in week one. Check in on day three, when the attention has worn off for everybody else.