Why won't my Kerbal respawn?

When I was going to land my rocket, the parachutes didn’t work and the lander crashed and Bob Kerman died. I didn’t know how long it would take for my kerbal to respawn so I waited for 2 months (in the game) for him to respawn but he didn’t respawn.

I’m playing on sandbox with easy difficulty and I set it so that lost kerbals would come back.