The reasons that drove some men to piracy to begin with didn't die with their pardons. Reasons such as lack of prospects on land, hope to make a good fortune and, or to provide for their family. Good former pirates didn't necessarily make for desirable candidates for prime jobs outside of the sea. Some men hoped to switch to privateering and either managed, had a bad go of it, or just decided pirating was preferable. Some men had been pirates so long, or at least sailors of a kind, that it was the life and job they best knew. That kind of acclimation could apply to men who had been reluctant pirates initially. The pardon was hard to turn down but that didn't mean it was easy for the men to stick to once they had it.

Stede Bonnet's motivations get tossed about in history. He wasn't always a pirate when he 'was a pirate', he spent awhile as a guest on his own ship after promoting Blackbeard to his captaincy. By the time the pardons came Stede seemed ready to leave the pirate life behind. Blackbeard didn't trust Eden enough to go without a test dummy and sent Stede ahead to test out the business of getting a pardon. Meanwhile he also marooned a portion of crew, damaged ships, and fled with a treasure that wasn't all his. Blackbeard got wind of Stede's granted pardon, got his own, got Governer Eden to grant him a privateering comission, and proceeded to be a pirate while Eden looked the other way.

Stede rescued the marooned men and either wanted to or was forced to seek revenge against Blackbeard. Which led to him either wanting to or having to return to piracy.

Rackham is a pirate who might have actually held to his pardon. But then he went and met Anne Bonny. She was already married to a man who worked as a pirate informant for Governer Eden. Neither pleading nor bribery would get Anne's husband to agree to a divorce, so Rackham and Anne fled to the sea in a stolen ship which voided his pardon. Piracy was the natural choice at that moment, and they didn't live long after.

Rackham, and probably Stede, didn't go back to piracy as a first choice. Whether Blackbeard ever actually intended to follow his pardon, he quickly lost interest, or it was a show and a way to get in Eden's pocket, we'll likely never know.

I don't know the statistics for other men returning to piracy after accepting pardons, and how quickly they did so. Whether it was many or few, the men flipping on their pardons were presumably not ones who'd had great success after returning to land or 'privateering'. Piracy was a dangerous business but ultimately it could seem the most profitable, reliable, and familiar enterprise for men accustomed to it and lacking better prospects.