Here are the buds that won't bloom.

It's just takes a little more time bloom. I can see these buds still have some maturing to go.

The buds don't seem to be maturing though after all that time.

could be what's called bud balling. It's unclear exactly what causes that problem but cool wet weather is one of the reasons. Just water in the evening and not during hot sunny days. I would suggest fertilizing but that's not what you should do in the height of the summer sun....

All you can do is be patient and hope it improves.

These were planted in a new flower bed so the soil is fertile enough and I water only as needed early in the morning and late in the evening when needed.
They are not soaked but did not dry out either.
I never water in mid day except for potted plants.

Are they in full sun? I have problems with a few of my coreopsis cultivars not opening or not blooming enough, but I think in my case, it is not enough sun.

Yes they are in full sun...as of today those buds still did not bloom :(

Its probably more to do with having been transplanted that stunted growth for now... Just be patient.. it may not bloom at all this season but it will by next season.. Keep the roots healthy. These things happen.