It doesn't matter how many friends you have, it is the quality of friends that counts. As you grow older friends will drift away as interests change and you have less in common. You will pick up new friends as you go along. When you reach old age if you still have one or two friends from your youth you are doing well. Also it doesn't matter if your friends are dumb, a little crazy, purple, martian, embarrassing or whatever as long as they are loyal and there when you need them is all that matters, the same goes for you.

Make friends. Not flaky ones that are only in it for their own gain, but ones you can count on, and vice versa. It's better to have a few good ones than hundreds of bad ones.

I wouldn't worry too much OP, this is probably the case for 90% of single adults who live alone. I have a fairly large friendship group but id imagine it would still take a month to raise any concern

To be honest, the average person spends more time at work than they do socializing with friends. Plus, work tends to have a steady schedule, meaning that the company knows if it is unusual for employee X to not be at work on Tuesday. On the other hand, depending on how close you are to your friends, you can be very close but not talk more than one a week.

You aren't wrong. If you don't show up for work one day, please tend to notice that more.

Mine too. I like it that way

Was there any discussion of the scenario wherein your home is invaded on the weekend and you go to work on Monday with a story of how you successfully defended yourself from criminals? If not, why not?

Surely this is the case for everyone? I mean, even if you have friends who see often, not hearing from a particular friend for one weekend isn't going to raise any alarm bells - you'd assume they've got other plans, or they've gone to visit family, or they wanted a quiet weekend etc. Whereas it's always odd if you miss work without calling in.