Intuitively, this makes perfect sense.

Non-lonely people interact with one another, continuously exposing themselves to each others views and opinions (even if indirectly).

A lonely person won't be part of this echo chamber, so their opinions will usually be self-formed and less influenced by the collective opinion of others.

It's easy to see how this creates a feedback loop. A lonely person doesn't share as many worldviews with non-lonely people, so has a harder time fitting in, which makes breaking the cycle even harder.