Why does this look exactly like https://pairdrop.net/ ?

Pairdrop is listed in the “Inofficial” instances section of Snapdrop’s GitHub FAQ

https://github.com/RobinLinus/snapdrop/blob/master/docs/faq....

Pairdrop is a fork with new features.

See: https://github.com/schlagmichdoch/pairdrop#differences-to-th...

Both look like Airdrop. Is this for people who don't have airdrop? I am not seeing the benefits.

Yes, as someone who doesn't use Apple devices Pairdrop is pretty useful.