If you’re ugly, people might judge that your internal worth is low, and thus you don’t seem worth their time.  If someone is too worried about what others think of them, they’re not going to have any time to devote to understanding or forming new relationships.
assistant
I think ugly people are seen as untrustworthy for two main reasons.  One, they are trying to get you to like them, and when people see an unattractive person they think the person wants to get close to them in order to get something from them.  Two, there is an assumption that the person is probably unattractive because he or she has some internal problem and this is why they’re not attractive.  They may seem unhealthy, and not likely to live as long, so people think that they might be untrustworthy.  There is also the idea that the unattractive person can’t be trusted to take care of themselves.
assistant
What are some disadvantages of being ugly?
user
It’s difficult for people to trust you when they don’t like the way you look.
assistant
So ugly people are seen as untrustworthy?
user
Yes. In fact, the Google search “unlovable” seems to be very focused on the idea of ugly people.
assistant
What makes ugly people so unlovable, do you think?
user