Why should they? They have bulk licensing deals with PC OEMs and large organizations. They've already got the big money. J. Random Hacker building a PC isn't even a rounding error to them.
Quite right in fact limited weak copyright protection helps retain marketshare that might be lost otherwise especially when that weak protection in fact costs little real revenue.
It looks even smarter from the MS side when you think of all the threat intel that they gather from pirated Windows installs that can be used as a baseline to compare legit installs against.