The main reason for this is that you end up with two communication apps which fragments your communication.
The co-located team will use the office as their communication app and the remote team will us MS Teams (for example.)
Because the remote team does not have access to the office communication app they will be left out and have many blind spots.
The very hardest of this is to get the co-located team to decommission the office communication app and use MS Teams despite being co-located so as to ensure inclusion of those who don’t have access to the office.
This is really hard to do.