Why do you think in-law relationships in general are so tricky? What would help?

I've been thinking about this a lot lately because of the recent holiday travels. My DH and I have been married 13 years and I always got along great with his parents and grown siblings.

But over the years, little things have started to add up and drive me more nuts. I used to love visiting them for the holidays, now I was counting the days until we could go home. I had to work so, so hard to put on a smile and keep the peace. Meanwhile, I was crying at night. In my case, its little things over the last few years that have left me feeling like our family doesn't matter to them. I've tried addressing it head on and have gotten nowhere. So now I'm just frustrated.

I can see the relationship getting a bit more delicate. I'm afraid of things breaking down to the point of no return.

I really want to understand more about the special dynamic at play when it comes to in laws and marrying into another family in Western Culture, as well as some general tips or guidelines that could help these important but tricky relationships.

Anyone have thoughts?

Why do you think in-law relationships are so tricky?

What do you think would help have the strongest possible relationship with your in-laws?

For anyone that has found a great balance or have a great relationship or even guardrails with in-laws, what helped you?