Maybe I can re-write that to make it more clear. The current explanation is “because he grew to fear what his followers had spawned”. So basically he realized he was creating clones with the same potential as him in life, except he is currently a ghost trapped in a dying clone. That isn’t going to end well for Palpatine prime - one of the others would take over. Perhaps he didn’t trust that his followers wouldn’t just betray him and begin following one of the other clones.

EDIT: Maybe jealousy is a better way to convey this idea over fear? “Because he grew jealous of what his followers had spawned. Those children had his power.”