Not sure why they don't suggest it. unless its to stop people mixing up different brands, so some don't compost. I still put them in the compost after tearing them open.

Well I find that very confusing - I'd have thought, if the glue contained plastic, THAT would have made it less suitable for a compost heap.What on earth are they using instead that its no longer advised?

Aha, just looked it up - the new product uses renewable plant based fully bio degradable material to stick the bags together, but they say it only bio degrades completely in an industrial composter. But if they used to seal them with plastic, that wouldn't bio degrade completely either... so I'm still a bit puzzled...

Funny, after making my kitchen a bit whiffy yesterday baking eggshells to crush for the garden, I was thinking I might just go back to a teapot & loose leaf.
On the other hand if you added sand or grit to your compost that wouldn't break down easily either so the small amounts of plastic in teabags may be best buried locally?

Must take at least a million to make a difference to a compost bin - I’ve learnt a little patience but tea bags ? Not me.