It's a huge privilege to have enough self-awareness and to be introspective enough to reflect on your own trauma, internal world, the way you relate to others, and enact change. It's a bit different if you've experienced something traumatic as an adult (e.g. a car crash).
It's not comparable to the impact on your psyche that significant childhood trauma has. Many people just don't have to psychological resources to deal with it alone. And how can they, if they've been abused and neglected by their own care givers? Our early years form our ability to deal with change, form relationships, affect our self-esteem, and so on. Some people get 'stuck' in their trauma, because they've spent an entire childhood flooded with stress hormones and hypervigilance. They need support and compassion to change. It would be like telling a diabetic to just try harder and produce more insulin.
And yes, some people are avoidant, but that's literally a psychological defence, that some people need support to overcome. Unconsciously, it won't feel safe for everyone to do hard work, make change, and address trauma. You need to feel psychologically safe to make any kind of change.
I'm a mental health nurse with older adults. I get people aged 80 who are still suffering with their mental health due to traumas that happened years ago. It's not something that goes away. You just live with it somehow. I've also had private therapy for years for my own childhood trauma, and it took a good couple of years of building trust and relational safety with my therapist before I could even begin to do the actual 'hard work'.
Also, and I say this working in them, mental health services are difficult to access and are not equipped to deal with significant trauma, which can take years.