Microsoft has strategic reason not to suffocate the other AVs completely. It's better to have multiple companies attack viruses on multiple fronts. If McAfee and ilk went away completely the onus would lie entirely on Microsoft.
Laptop manufacturers are also to blame because product bundling and bloatware are nothing new.
Microsoft on their part could make it so that Defender worked alongside McAfee but that might encourage users to buy McAfee even more, arguably (double the protection or not knowing they are already protected).
Lenovo are particularly egregious. They collect data from Conduit via their toolbar add on (Conduit is one of the worst malware makers out there - they are owned by Perion/CodeFuel). Lenovo refuse to disclose they do this, in fact I have support emails denying they do.
Laptop manufacturers are also to blame because product bundling and bloatware are nothing new.
Microsoft on their part could make it so that Defender worked alongside McAfee but that might encourage users to buy McAfee even more, arguably (double the protection or not knowing they are already protected).