Here's why:

* Gravitational Pull: The gravitational pull of the moon and the sun are the primary forces driving tides.

* Alignment: During first and third quarter moons, the sun, Earth, and moon form a right angle. This means the sun's gravitational pull is acting at a 90-degree angle to the moon's pull.

* Combined Force: The sun's pull partially counteracts the moon's pull, resulting in weaker tidal bulges and lower high tides (neap tides).

In contrast, spring tides occur during new moon and full moon phases when the sun, Earth, and moon are aligned, resulting in a combined gravitational pull that creates stronger tides.