Bottom bracket needing repacement more often in a single speed bike
It is inevitable than with more radial load, bearings will have lesser lifespan. The only alleviation to this is to get good quality bearings.
If you notice a decrease in your bearings' lifespan, check if you've fitted your bottom bracket properly and specc'd everything to more or less proper torques indicated. If bearings fail regardless, there may be misalignment either on your bottom bracket unit or the BB shell itself. (more likely the latter)
Due to the larger forces inputted, the misalignment's effect of degradation is aggravated.
@juhist 's option for outboard-bearing bottom brackets only serves as a non-direct solution and masks any genuine issue the drivetrain has.