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One of the themes in RWBY is about the current generation being failed by the previous one. We see it a lot with the mess that is the Xiao Long-Rose-Branwen family.

Every single member of Team STRQ failed Yang and Ruby, to a greater and/or lesser extent.

(read more cut because this gets long, although I make no promises that I'll cover everything, and please forgive any typos, I'm very tired)

Raven abandoned her daughter and her husband (yes, husband, according to 'The World of RWBY' book by Daniel Wallace, written with input from CRWBY), and the rest of her team. Yang wasn't old enough to remember her, and may well have still been a baby at the time. The reason why seems to have been for Raven to take the leadership of the Branwen tribe of bandits, although I think it was more complicated than that, which would fit with Raven being such a complicated woman.

Summer. Yang's super-mom. The mother who stepped up. I deeply respect that. She had the best of intentions when she left on that super secret mission with Raven, presumably to confront Salem. To protect her family, and hopefully so she'd never need to leave them again. Unfortunately good intentions pave the road to hell, and she ended up never going home to her girls. That truly tore the family apart, and it never really recovered. Yang's abandonment issues aren't only from Raven leaving, and a lot of Ruby's issues come from trying to live up to the memory of Summer while being held to impossible standards.

Tai didn't react well to the loss of Summer. To quote Yang: he shut down. Yang had to pick up the pieces and keep things together. Alone. Because Tai was always busy with school, and Ruby couldn't talk yet. It's striking that Yang refers to her dad by name in Alone Together when talking to Weiss about it. Most kids don't do that when referring to their parents. Your mileage may vary about what that means, but to me it sounds a lot like resentment. Don't get me wrong, Yang loves her dad. But it's entirely possible to feel both love and resentment.