In-laws not attending baby shower...d

I need some different points of view here. My husband and I have been together for almost 9 years and married about 4.5 of those 9 years. I have 1 child from a previous marriage. This baby is my current husband's first blood child (he treats my daughter as his own and he is currently in process of legally adopting her). This will also be his mother's first blood grandchild (his father has another child who already has kids). His family welcomed me and my daughter with open arms from day one and there's never been any issues that I'm aware of. My husband and I wanted children but I was diagnosed with pcos and was told it was a miracle I'd ever even had my daughter and my chances of conceiving another child without some type of fertility assistance was almost 0%. I became really sick about 1.5 years ago from issues due to Crohn's disease... in and out of hospital and multiple surgeries/procedures for almost a whole year. When I finally started getting better and things began looking up, we found out I was also pregnant which obviously makes me high risk. My friends and family are throwing us a baby shower (our families have always gotten along too) but my husband's parents informed him that they had "discussed it and have decided to pass" on going to the baby shower. I just don't understand and neither does my husband. They've already given us our shower gift early but because of the type of people they are, I just can't believe that they wouldn't show up just as support for their son's first and only biological child. Anyone have any thoughts of what could be going on? We are both beyond hurt and upset...

UPDATE: The shower isn't for another month and they do not need to travel. We actually went through the trouble of finding somewhere close to where they live (maybe a 3-5 minute drive if that) so that travel would not be an issue. My husband expressed his feelings on the matter and all they would say is that they "just decided to pass". They won't explain any further...