It could be any number of reasons:
Assuming there are no problems with the soil and the seed is not buried too deep then the main things that effects germination are water and temperature.
If it's unseasonably cold and wet, your seeds may rot before they have a chance to grow.
Bird might have eaten them.
With mixed seed packs, the plants will all have different germination times, anything from a couple of days to a couple of weeks. Patience is required.
Unless you are planting a large area I’d be inclined to sown seed indoors in separate biodegradeable pots. Paper ones are cheap and easy to make. Use biodegradeable ones as some wildflowers don’t like having their roots disturbed (poppies especially). You can just pop the plant in its paper pot in the ground and it will degrade naturally.
Even if you are planning a large area, a trial run in a few pots might be a good idea just to test that the seed is still viable. It’s generally recommended to store wildflower seeds in a cool, dry place, ideally in a refrigerator, to extend their viability. This helps prevent moisture from damaging the seeds and ensures they remain viable for longer periods. If seed is sold loose in a box or packet you won’t know how it’s been prepared, packed, transported and stored.