I’ve heard that Marco has a few financial deals that are very questionable.
Jeb made a career off his family name. He really hasn’t offered much else.
In addition, Jeb seemed to prefer deal-making with business interests to building public support and pushing for wide-ranging reforms. For example, Jeb's proposed state ethics law reforms were quietly shelved by the legislature without a peep of protest from Jeb. He never developed a good relationship with the legislature, often seemed high-handed in attitude, and, instead of seeking talent and experience, tended to prefer to run his administration with personal cronies and young aides, who were generally known as "Jeb's kids."
If elected President, Jeb would be a "low energy" reformer and would make deals within the existing political game. He would likely soon have a conservative revolt on his hands and thereby put his reelection in doubt.