Thread: why do some Scottish marriages have witnesses and others not?

I'm trying to decipher a marriage record from Scotland's People.
There are two marriages on the page; one has been signed by 2 witnesses and the other just says 'warrant of sheriff (unreadable) of Lanarkshire'
Does anyone know why?!

Thought I'd just add: my great-grandparents marriage was not witnessed, but I noticed my g-g-grandmother was a witness in the other marriage on the page.