why does Bassanio ask Antonio for money and not others?

Antonio actually offers to help Bassanio before he asks him for money. Bassanio was discussing his plans to clear his debts, and Antonio said he would do everything he could to help him. This offer has everything to do with love and friendship.

"I pray you, good Bassanio, let me know it.

And if it stand, as you yourself still do,

Within the eye of honor, be assured

My purse, my person, my extremest means

Lie all unlocked to your occasions."