Windows kill Mac? Since when? Windows is an OS, Mac is a hardware platform. MacOS X is an OS that run on Intel-based hardware which is totally different from System xxx that run on PowerPC & previously M68000s.
Macs are around and is very profitable. PC manufacturers such as the ex-number one Compaq are no longer around. HPE jettisons its PC division. IBM jettisoned its ThinkPad division. Dell became a private company.
Macs have never been big in market share. In fact, looking at absolute number of units sold, installed base of Macs have been growing
Having its own device, Google can better control the users and obtain higher price from advertisers.