That's because Facebook is a SOCIAL network. Even though it has evolved over the years to allow for business pages and even sales, it's STILL a 'social' network.
You can still join groups...whether 'public', 'private' or 'secret' and still have your personal stuff remain personal/private if that is what your settings are...like mine. As an example, I belong to a knitting group with 7.2k members and a local 'happenings' page with 34.2k members and unless I am 'friends' with someone in that group, they can't see what is going on in my personal life.
Your only other option is to do what
@KiwiMoose suggested...have a second personal account with a second email address and then only use it for business (you HAVE to have a personal account to have a business page). Note that you can't be logged into both accounts at the same time unless you use separate devices (I used to have a second account for playing games).