The NBT tag ExplosionPower on Creepers is a byte, rather than an int. Therefore, it overflows at 128, resulting in explosions that don't destroy anything.

This is inconsistent with Ghast fireballs, which store their ExplosionPower as an int.

To observe this for yourself, use the following commands after spawning a Creeper (with doMobSpawning false):

  Creeper explosion:

data merge entity @e[type=creeper,limit=1] {ignited:1b,Fuse:1s,ExplosionRadius:127}

  Fireball explosion:

execute at @e[type=minecraft:creeper] run summon minecraft:fireball ~ ~ ~

kill @e[type=minecraft:creeper]

Replace the number after ExplosionPower with the desired value. To avoid lag, make sure doTileDrops and doFireTick are both false.