Strange word to choose for closing down a campaign. Maybe many of them hope to leave a little window open.
Supposedly it has to do with paperwork. If they quit, the campaign has to turn in financial paperwork within a short period of time. By suspending the campaign, they extend that timeframe significantly.
At least, that’s how my hubby explained it after hearing it on NPR. He apparently tunes in when he’s driving to hear what the other side is saying. I guess he has a much stronger stomach than me, lol.