I takes very little concentration to ride a bike. I does take a bit more to track traffic, but otherwise its roughly the same level as walking.

So, it you're not able to bring at least that wee bit of focus, I wonder about your general ability to stay alert and focused on whatever you're doing.

Unless you can account for why you're losing concentration, and especially it it's also happening off the bike, and/or if this is a new thing for you, I'd see a doctor to see if there's something that might account for it.