I hated it too. When I first moved out (19-ish) I moved in with 4 people into a big Victorian House, (9 months I stayed,) then I moved into a flat share with 2 other women. (Stayed 15 months.) 2 years with other people. Then I got my own place. Stuck it for a year. I was really bored and lonely on my own, and was always phoning my parents, my cousin, and one of my friends. Was harder financially too. I moved back to my parents at 22, then met my now DH shortly after that and moved in with him at 23 and a half. Lived with him ever since. (Over 30 years!)
I think women who are very happy alone are far more likely to be people aged 45-50+ who have been in rubbish relationships. (For many years.) Most people I know who are younger and never married, have no desire to be alone forever. Why on earth would anyone want THAT?! 
As has been said, that myth that single women are the happiest is a load of shit. It was done via a survey YEARS ago, with about 1000 people participating. Single women have clung on for dear life to this load of bollocks for YEARS now, to try to convince themselves that they are happier than married women. Methinks the ladies doth protest too much! 😆
As a pp said on another thread almost identical to this! (bedeepkoala)
As far as I know, the entire myth is literally based on a single sentence that some random academic said at a low tier conference which the Guardian picked up on and endlessly repeated since it fits their agenda.