In 1987 vehicle manufacturers were struggling to meet the emissions standards
Valve overlap, while a performance gain, is not necessary for an ICE to run properly. Valve overlap will allow un-burned fuel to scavenge the combustion chamber of carbon dioxide to ensure a well oxygenated air/fuel charge.
Emissions standards drive much of the engine and electronics design in vehicles. Due to the heavy restrictions that were being implemented in the mid to late eighties many manufactures took valve overlap as a performance attribute out of the designs of their vehicles.
Other components you see on this era of motorcycles include:
Carbon canisters for fuel tank evaporation and hydrocarbon leak prevention
Retarded timing to allow for a complete burn of the air/fuel charge
Restricted exhaust systems
Restricted air intake systems
Along with a zero overlap cam configuration the above items assisted engineers and organizations to meet the newer regulations that were set for enforcement as emissions standards slowly came online throughout the world.
There are several other models of Honda motorcycle with no valve overlap in that era.
Honda GL1200 Goldwing
Honda CX650 Silverwing
Honda V30, V45, V65 engines in the Sabre, Magna and Interceptor
Many more models from Suzuki, Yamaha and Kawasaki also used this in their favor for adherence to the regulations.
There are quite a few cams as well as slotted cam gears/sprockets for you model of motorcycle that can be implemented to put a little valve overlap into your configuration. The performance gains are fantastic along with a high performance exhaust and carburetor jet kit.
As an aside. The reason your motorcycle is a 700cc and not a 750 is due to the Danforth Bill from the Missouri Senator of the time. Heavy tariffs were implemented on motorcycles 700cc and higher to assist Harley Davidson sales after their bankruptcy of the time. Your bike is actually a 698cc engine.