You cannot figure out why?
Allow me to explore. Sometimes my clients say they haven't grieved for various reasons... not wanting to feel the emotions and putting a lid on them... getting on with life and keeping busy so never thought about stopping to grieve... unable to grieve due to complexities in relationship with the deceased e.g. abuse from a primary care giver.
Grieving is very important but not the answer for everyone... for some people grieving doesn't help them... so it's about figuring out what might help you... you start by trying. If you notice you are hesitant and don't want to for example, cry... then you need to grieve.
When we don't grieve sometimes emotions can catch up with us... and bite us in later life.
How do we grieve? For someone who hasn't been able to cry or forced themselves to stop then crying is one... writing can help... writing a letter to the person you lost stating how much you miss them or what they meant to you... visiting places you stopped going because it's too painful a reminder... could be a beach you used to meet your loved one at. It could be meeting a close friend or family member of the person you lost to speak with them... remembering anniversaries... many ways but the point is to not block the process. Not to label the processes as something anyone else would be fine with... not to blame yourself or hate on yourself for grieving.
This might help. I recommend it to some of my clients:
https://www.amazon.com/Chicken-Soup-.../dp/1623611016
So in conclusion you may not have grieved because it didn't feel right, you blocked it, or didn't make time for it... or thought everything was okay and got on with life (or something else) but... even if everything seemed okay it is important to grieve. It's good you are asking questions and identifying you haven't grieved. Why haven't you? Too painful? Too busy? Not sure where to start?
Good on you for acknowledging you haven't grieved. No you are not abnormal. When we experience multiple losses it's sometimes difficult to know where to start. Many of my clients say it has been too much to acknowledge when it comes to multiple losses so they get on with life. Some fear they would fall apart if they commenced grieving. You won't. It might feel painful but in life... without the mud there can be no lotus. The lotus is a beautiful flower but it wouldn't be what it is without the mud and crud beneath it... that helps it to grow.
Grief therapy with an approved counsellor is also worth considering. Especially if you think or feel a lot of anger about your losses and don't know how to express it.
Hope this helps.