I couldn’t tell from the original post- have you formally invited them to your house to meet the baby, and they refused, but would agree to see you only if you brought the baby to them?
I think the shower thing is tricky- in the past, I have typically seen someone from the mom’s side host the shower (grandma, friends, sisters, aunts, cousins, etc). Maybe your in-laws didn’t want to overstep (if you are not normally close) and host the showr, thinking someone else would? Maybe by the time they realized there wasn’t going to be a shower, it was too late to put one together?
If you’re not normally close, I think it’s wrong to expect or assume that they would throw you a shower, visit in the hospital, come over multiple times to see and help with the baby, etc. They also may be offended that you didn’t attend the Christmas party. Maybe they had gifts to give the baby then?
Some families aren’t super fussy with babies, aren’t into visiting eachother often, etc. It doesn’t mean they are doing it to be mean to you, it’s just not the way they do things. They may also think that you need a few weeks to adjust to the baby, and are just trying to give you time and space. With the baby being born right before the holiday, it’s also tough timing.
If I were you, I’d invite them over for a meal & to meet the baby. Make it breakfast with just some bagels, coffee & OJ, or dinner with pizza. Whatever is easiest for you. Set the date, set the time, and see what they do.
If they don’t want to come (which would be totally strange to me), then chalk it up as a lost cause and move on. It won’t hurt yourfeelings if you’re not expecting much from them.