Why does coolant leak through the temperature sensor??

I don't recall ever seeing a temperature sensor itself leak. So I'd suspect you're seeing a leaking seal or cracked housing.

That was a common problem with the old style sender, they just had to be replaced. I have never seen a temperature sensor leak unless the seal had been damaged, I have seen some that had the sensor in the thermostat housing where the housing had a hairline crack where the sensor was screwed in leak.

good'">

Check the rubber seal where it is clipped into place. Was the part a pirate part. Try a genuine Ford part.