Split family Christmas gifts

So my parents divorced quite late in life when my siblings and I were in our early 20s. I have 2 younger siblings and my dads partner has 2 children about the same age. As a family, my side has always loved giving presents and Christmas is a big deal but last year my step siblings decided we should do secret Santa - awesome, no problem, half of us also have partners so there's a lot of people to buy for so let's cut back. Then my dad and step mum decided to join in on it as well. No problem. It all went by fine, everyone got their gifts and it was great. Then I've found out that my step siblings still bought the parents a sizeable gift (outside of secret Santa) and the parents bought them sizeable gifts too (again outside of secret Santa). I don't care about the gifts at all - were all adults and stuff isn't so important but I do care about being made to feel like the "secondary" side to the family. I feel like it's unfair on my siblings and I. We would have happily bought for the parents but we had all agreed not to? And obviously their mum (my step mum) is the one who bought them the gifts and she can do what she likes with her kids but then we should just do it entirely separately right? Am I being unreasonable? (On a side note, if I am being unreasonable hopefully my irritability over this is a a sign of early pregnancy HA!)