Adding members to Agenda but unable to because they are grayed out

I sometimes edit the Agenda and assign members to roles but this is the first time that I noticed a few active members are grayed out and I cannot add them.

Can you tell me what has changed and how do I rectify this?

They have said they are not attending the meeting to you can not add them to a role.

I see that makes sense.

Thank you!

Is there an area where I can see that they said they were not coming?

Edit the Agenda and click the Attendance tab