Inheritance - has something shifted?

If I'm not mistaken OP, they're using trusts to ringfence their estate from the partners of their children right? Presumably to protect their money becoming part of a divorce settlement. I think some pp have missed this.
In that case, hand the reins over to the 'blood' relatives and let them handle things going forward. If you feel strongly enough about it, come Christmas, let DH handle the presents and don't bother hosting them.

The In laws see that you think their son is crap and you are surprised?

as others have said, their money their choice and you choose to do the things that you did for them.

Also, it's quite normal for people to leave their money to their relatives.

I’m always one to say, their money their choice when it comes to wills.

But I do understand why you feel a bit miffed. I’d see it as, you’re good enough to do the heavy lifting for them, but not good enough to warrant a mention on their will. With this in mind, you’re completely entitled to scale back any help and leave it all up to your dh. Depends how unappreciated you are feeling at the moment.

Nothing has changed. It's totally up to them who they leave money and how their will is arranged to and it always has been..Some people have always used Trusts some not.
I am a little confused about why you think your in laws should leave money to you though surely it's natural for them to leave it to their children.
I don't know if you have children but if so wouldn't you want to leave your money to your children rather than go their partners?
My in laws didn't have any money to leave but if they had I wouldn't have expect any of it.
I'd expect it to go to their children.

Time to hand the reins to dh.

their money their choice.

It is also your choice to have been doing the wifework instead of letting their blood relative son do it.

So: stop doing all the things, any of the things, for them. And/or tell them that you will be the one choosing their care home so they might want to reflect on that...

Ambulance chasers seeing a revenue opportunity after car finance, housing repair, damp. spray foam and so on have all had problems. Clams farms and the legal sector are seeking new revenue streams and advertising on daytime tv. Daily Mail publish articles about the Chancellor taking their money and care fees and evil divorcees. One bloke down the pub does it. Sometimes things achieve critical mass.

The sad thing is the two times (probably linked by recommendation so not a reliable sample) non wealthy (£10m plus who can afford and got decent advice) people I know did this and I asked them to describe what they'd done, it was clear they'd not protected their home from care fees but had really screwed things up by using a dodgy firm who inserted themselves and who had previous form for fraud. One chap went to speak to a reputable family solicitor with instructions what to ask, the other refused to listen. The actual instruments were cynical and substandard and didn't even hang together well. I was curious so looked at some more reputable firms and most wouldn't achieve care home fee protection. I didn't look at the divorce protection.

I would never expect my in laws to leave me anything. Surely that’s unusual.

Probably they have seen something in someone elses family, or fear something in their own where maybe one of their children gets divorced and the ex ends up with half the money.

It's their money and their choice. Just as how much time you spend on them is your choice.

What happens to the money you inherit, and does your husband agree that should be ringfenced for you as a blood relative to your parents ?

Having bought Xmas presents, hosted and done heavy lifting for 30 years when their son is crap I am a little miffed.

Understand where youre coming from, but this statement is coming across as though everything youve ever done os purely transactional, we know thats not the case with a long marriage etc but you could stop all the heavy lifting, no more, let DH deal with all things for his side from now on, and if they mention it say ah, I'll let your blood relatives deal with it.

Not a generational shift, but does sound like something has changed, do they think a non blood relatives somewhere is on the verge of divorce, or is horrible, or they just don't like?

Their money, their choice. This is literally the only response ever needed on any discussion of this sort, and one you will never listen to.