Normally healthy plants will shed flowers to maintain the balance. But the drying and falling of more flowers may happen for several reasons, like
Temperature: Fluctuation in temperature generally causes flower drop, especially high day temperature and low night temperature.
Excess application of fertilizers, particularly nitrogen fertilizers or lack of certain nutrients may also causes flower drop.
Moisture stress: Fluctuation in water, i.e., excess watering or low soil moisture also cause flower drop.
Pollination problem: Pollination mainly depends of insects (bees, butterflies). Poor pollination causes flowers to dry and drop. So if your garden is lack of bees you should go for hand pollination using cotton buds or small paint brush.
Spacing: High plant density may lead to poor air circulation resulting in flower drop.