Why Wizards accept:
3 first round picks and a good young player with potential is a lot for an aging player in Bradley Beal, they should probably accept this trade because they probably will not get a much better package for Bradley Beal. The only downside is that they take in a bad contract in Evan Fournier but they can maybe work out a buyout for him.
Why Knicks accept:
They have a lot of first round picks to give so 3 first round picks isn't a lot, also Bradley beal forms a great trio in New York with Julius Randle, Jalen Brunson, and Beal. They shouldn't think too much about this. Also Gary Trent Jr is a nice signing. (I didn't work hard on the contract but you get what I mean.)
STARTING FIVES:
Knicks starting five:
PG: Bradley Beal
SG: Jalen Brunson
SF: Gary Trent Jr
PF: Julius Randle
C: Mitchell Robinson
Washington starting five:
PG: Monte Morris
SG: RJ Barrett
SF: Kyle Kuzma
PF: Kristaps Porzingis
C: Daniel Gafford