After reading some of the other comments, while I agree that some writers do actively write stories about overcoming loneliness and finding connection - it seems really more of a plot device/trope than the writer trying to be deep.
In the heroic journey, the MC has to have some defining moment that pushes them onto their journey. There also has to be something that prevents them from going back to their previous life. For example, Luke Skywalker HAD to lose his aunt and uncle to set him on his Jedi journey. They couldn't just be lounging around at home for him to come back to.
But unfortunately, the plot device has warped into the trope of "MC is always lonely, orphaned, abused" as an instant way to garner sympathy. The Dursleys HAD to be horrible to Harry to give him proper grounds for abandoning the human world in favor of his new world. Ron is the convenient instant bestie who shows up to help teach him about the new world. Hermione is the token girl bestie that has to be in the dynamic. The MC's loneliness officially goes away when they either find out that they're biologically related to another character or they pair off with one half of a sibling set, making the group all related.
It happens in a ton of genres. Werewolf romances - the MC is always abused/orphaned so she can leave her terrible life goodbye in favor of the better life with her lover. Shifter romances - the MC is now an adult, but she's an only child, parents sick or dead. Her bestie betrays her so the MC has no ties to her previous life. Even Twilight did this, Alice's singular role is to be Bella's vampire best friend. Bella happily isolates herself from her old life to dedicate to her new life.
MC needs to meet a mysterious group of people who change their lives - someone's the awkward new kid. If their partner is the new kid, the MC has little to no friends to stop them from getting involved in the plot shenanigans.
Even Disney is guilty of isolating their protagonists. The vast majority of their princesses are socially isolated. It's a large part of Elsa and even Belle's personal story arcs. I don't think it's necessarily "wrong" to include loneliness and isolation in your stories, but I think you should look past it as a quick character "flaw" to give your MC. One of my favorite versions of Beauty and the Beast, she has a loving and supportive family/community to go home to. She still struggled with self-doubt and a desire to fit in, but her choice became 10x more impactful because people missed her when she left. No one "saved" her from her loneliness but she grew out of those feelings as she developed as a character.