My MIL and FIL paid a lot towards our wedding, and my parents paid for the reception (buffet in our local).
My DH was an only child and I think my in laws were glad to be rid of him! (joke), but my MIL did say that there were no other kids and she wanted to do it.
My Parents had previously paid for my sisters reception and also did the same for my youngest sister, so we didnt find it unusual for them to do it, but we certainly didnt ask.
We also had our own place and our DD when we got married, so to help, family also helped instead of giving us presents. I had bagpipes and drums (DH aunt and Uncle), Cake (my aunt), Flowers (another aunt), cars (uncles), Hair (cousin) among other things. I would never have expected my parents to pay for any of it. The fact that they did was nice though, and the fact that family helped in some small way made it feel more thoughtful, than just buying a gift
Maybe if you want to feel involved, but dont want to contribute money wise, maybe offer to do favours, or something else that involves time but not money.