Even we have had trouble, as have large scale re-wilding projects. So don't feel defeated.
In many parts of the UK - particularly the East - we have had the driest and hottest combined Spring and Summer, on record.
The fact that the Spring was dry, made the establishment of new plants (whether from plugs, or seed), much more difficult. Some made it - the toughest ones - but many will have withered - just as the grass did from mid-June.
Have heart - it is a well established fact that meadows and wild areas take 3-5 years or more, to get to their best.
It's no different to any other part of the garden. It takes time.
By way of 'professional' advice, I'd say we simply need to start adapting to what is already here. Global warming. It's not a policital statement; it's scientific consensus, so what can we learn in terms of wildflower meadows and wildflower habitats?
Well, it tends to support a trend towards Autumn planting of perennial wildflowers. The advantage this gives over Spring planting, is 6 months of root-growing time (albeit slow over winter). The period October - March is rarely dry, even in these changing times. I'm certainly going to weight my planting at scale, towards Sep/Oct/Nov.
Spring and Summer planting is perfectly possible at a smaller scale. You just need to water. A full soak, weekly, unless it properly rains.
Many of the failures I've heard about this year, were caused by the prevailing attitude that wildflowers should just be 'left', to suffer whatever nature offers.
Well it's true that once established, most can cope with drought, it's worth remembering that establishment itself can take a full year. Especially in grassland and around trees, where theses dominate the water availability and root-space.
So, stick at it, keep planting, and clump by clump, individual by individual, they'll get established, and begin to spread. It might take 3 years of planting, to get it where you want it. Sowing, can take up to 7 years to get right.