I don't carry a multitool on a solo trips. I look at the bike in detail, screw by screw, etc.... :

- What do I know how to fix:

- What exact tools would I use for all the fitting on my bike that relate to stuff I can fix;

-Then I review, and toss stuff out based on weight, the likelihood of it actually breaking, my ability to fix it on the road (or to find a missing tool like a really large wrench while on the road). I also look at stuff like whether I would need two of a kind of separate tools to do various things. And I look at whether particular tools have the guts to actually get the job done whether they fit or not. Pedal wrenches are required to use railway boxes around there, and they need to be substantial.

When making up a fancy bike where you get to choose all the stuff that goes on it, you can make the tool kit much smaller if you carefully choose the parts on your bike. Stuff like straddle cable holders can use several wrenches or one Allen wrench that fits a lot of other stuff.

Generic tools like a multitool, other than being pacifiers, might come into their own when riding in a group, where the stuff on them might actually be on someone's bike. Still I normally find individual tools lighter, and more useful, but then that would also depend on how closely a specific multitool matched your bike. You might have a near perfect fit and function match, and that could explain why some people like them.