Both Agarita (Mahonia trifoliolata) and Mexican Buckeye (Ungnadia speciosa) are typically very reliable for flowering and fruiting, so you're seeing something a bit unusual. Both species flower early in spring, so it's possible cold weather could play a role in them failing to flower some years, but it is doubtful freezing would kill the developing flower buds of these plants every year. Of course, if there are no flowers, there naturally be no fruit following.
Most often, lack of flowering is an indication of too little light, in other words, too much shade. We know of no other factor that would likely be the cause of the problem.
