The program it replaced didn’t do this, hence the surprise. You could be using the old program, and one day windows update it with this new program, and suddenly your passwords are uploaded to Microsoft cloud service when you launched it. People would similarly surprised if K-9 mail upcoming replacement, Thunderbird mobile, suddenly store your password in the cloud.
I don’t see how this is any different from adding another e-mail account on gmail.
The program it replaced didn’t do this, hence the surprise. You could be using the old program, and one day windows update it with this new program, and suddenly your passwords are uploaded to Microsoft cloud service when you launched it. People would similarly surprised if K-9 mail upcoming replacement, Thunderbird mobile, suddenly store your password in the cloud.
Configuring local software vs delegating to a web service