In laws vent

My oldest has his 6th birthday today. My youngest newborn (of 4 kids) is 1 month old and my in laws have yet to meet her. My son just wanted his family and 1 friend from school to come over for lunch and cake today. This morning, my husband's parents, as well as his sister and husband and 2 kids canceled because it's a rainy day. They don't want to drive in rain. Only my husband's brother will come from his side. The party is indoors and they only live 40 minutes away. It's barely drizzling out. Honestly it just hurts because for whatever reason they only come for birthdays (they won't come for other holidays even though we invite them), and my son was really looking forward to seeing them on his bday and introducing his new sister. It just feels like a lame excuse and they're always coming up with excuses to not come even when we invite them just because, they're always "too busy" or "we live too far" (it's 40 minutes and they're not disabled or anything). I'm trying to stay in a good mood for my son, but I'm upset and I can tell my husband is too. Anyway thanks for letting me vent. In laws suck.