I just always assumed most were alts but never really gave it much though, op.
In my case...This account now, though my main, is still technically an alt. Its the third I created. The first I lost details to, and the second I moved on from wanting to get away from my 'human roots'. I never plan on adding my card details to this account because I never buy anything. I transferred about 4700 Lindens I had from my old account to this one, and that was more than enough to buy my current bird avatar, and I'm perfectly happy with just having this. I did remove my payment details from my old acc