MAF staff are unable to use Teams when they can’t connect to a Microsoft server. Microsoft servers are not in every place they need to be. Matrix reduces connection problems by installing a local homeserver close to the users it serves. Even if the ISP is down, users can message within the office.
Teams is a “walled garden”. You might like Teams at headquarters, but the field offices may not. The Matrix protocol was designed to encourage “bridging” between other protocols. Element Matrix Services (the sponsors of the Element brand Matrix clients) offers such a Matrix and Teams bridge service. That service is commercial, because Teams is.