MS people frequent this site. Maybe one of them could get some detail on the subject?
This is where I strongly prefer the Apple way of signing in with a normal account and -- if you choose -- linking it to an iCloud account. This is very different from the Windows style where MS accounts take over your local login.
You don't have to use a MS account. You can use a local account. 10 is different from windows 8 in that regard. You can take Cortana off the taskbar. Use a different browser in incognito mode all the time. Store your encryption keys in a TPM, smartcard, or Active Directory. There are actually lots of options. You have to actually look into it though.
Literally all of the people who install it or buy a PC with it installed have the choice of making that decision or purchase.
And you're right, they won't change the defaults and that's not a travesty of some kind. It actually really doesn't matter to most people. Not because they don't understand it. They do, and they want to use it for one reason or another. People in our technical circles overestimate the importance of this stuff by some fairly crazy amounts.
These problems are not mutually exclusive. They are all serious problems.
And you seriously think most people know what that stuff means?
"Oh! Gee thanks Microsoft. Record everything I type in the operating system to make your autocorrect better" or whatever the hell they do with it.
They absolutely do not then realize that when they named a file "my-pot.jpg" and then search for "pot" in Cortana (which is stored by the way.. even for local searches) that information could be used against them in the future.