Someone has to pay for that work. Either volunteers are donating their time, corporations “donate” work of their employees or hire it out because use of the project generates profits for them and they recognize not everyone can be a parasite (The FOSS model)
The other alternative is users paying directly.
If you want to use a closed source os, then pay for updates or you will be monetized on other ways. (In the case of MS that would be ads or the OS is just an incidental product used to drive sales of software or cloud computing)
Alternatively they are using google and their webmail client, no windows mail needed.