Are you certain they are flower buds and not seed heads? Many of my Dianthus have no seeds in them this year, but the seed heads just look like unopened flower buds.

yes I agree with Owd, old flowers where the petals have dropped look like buds.
when I buy carnations/pinks in the local supermarket I squeeze the buds and if firm I know they are fit to flower.

You didn't do anything wrong. Dianthus is described as a biennial or short-lived perennial. They are very tender and susceptible to a myriad of problems. Allow it to self-seed in the garden to ensure its return the following year or sprinkle new seeds. I grew carnations a couple years ago. It was such a stunning plant with a sweet/spicy aroma wafting across the garden. Maybe give those a try. They'll give you 2 years.

It may also be a tiny caterpillar called a budworm. Their tell-tale is a tiny round hole in the side of the flower bud.

Sorry to disagree, but the type of Dianthus mostly grown in Britain are reasonably long lived reliable perennials. The ones in our previous garden were still flowering well after 20 years. Brought some of them with us as cuttings when we moved here and they are still flourishing.
There are biennial Dianthus, D. barbatus, D. alpinus etc are but there are many good perennial ones.

.....and many readily self-seed so you think they are the same plants but actually they are the offspring and the parent plant died out because of the problems we are discussing.

Thankyou everyone. I don't know what kind they are but they smell gorgeous. I'll take some cuttings as I'm not good with seed. I can't see any holes at the side of the 'empty' bud Tug. Owdboggy they have no seeds in them; they are completely empty.

Since many of the named forms do not come true from seed the original plants must have survived for them to produce the same flowers each year.

I have one that I took from my mums garden when she died over 25 yrs ago and when it got too woody after 10 yrs I just took cuttings, so they are identical to my mum's plant. It is a very double flower and rarely forms seeds.

Merlinbd they may not form seeds if fully double or if they are the single ones the weather might have been too poor for the pollinating insects to do there job.

Thanks Owd and SBG. There hasn't been much sun this year has there. My figs are nowhere near as ripe as they usually are at this time of year.
Thank goodness it's so easy to take cuttings; and slugs don't enjoy them.