What happened to them?

MariaBBB

yesterday

This could have been caused by some insects such as mole crickets could have eaten the seeds. When tunnels from these insects are seen, a pesticide bait, granule or liquid can be used for control.

Seeds planted too deep may germinate but may not have enough food reserves to make it to the soil surface. A general rule of thumb is to never plant a seed deeper than twice its width.

Too much water could have rotted the seeds or aggravated soil-borne diseases which killed the seedlings.

Or a dry period could have caused the developing seedlings to die.

Also, the seeds may be too old. Always use fresh seed. Check the viability date on your seed packets