This is, in fact, the point. They do not want the support burden and negative security posture of supporting billions of computers that cannot have a locked bootloader.
Linux has no problem supporting pretty much every PC hardware ever made, any filesystem, etc. So while it might reduce their costs, they are hedging customers every generation
Linux Foundation doesn’t “support” anything in the sense met above. They do not provide antivirus updates, or a help line, or consultation services. They are not responsible in any way if every device running linux gets hacked. It’s simply not their problem — but it is Microsoft’s.
I get that security is part of the posturing - I just think it is tone deaf to the reality that not everyone is going to be willing to spend $500-$2000 USD just to be able to "run" Windows 11.
I have friends and family that will continue to run EOL Windows 10 which is worse unless I convince them to migrate to Linux.