The penetration in that area becomes very noticeable and may only be patched out. Once the film starts wearing it becomes harder to keep the heads from hooking. Synthetic lanes are laid on top of existing surfaces, often with no structural work done. After 30 to 40 years of abuse, foundations take hard beatings. The topography of the lane is more likely to change and sometimes it can cause drastic differences in ball reaction.
Some lanes shift with each passing train.
Many times you can see the lane bounce when the ball impacts. This creates higher friction and can also cause the surface to wear faster. Synthetic lanes do not provide any more of a benefit than any other surface. Each has its own problems. This can have a great effect on the bowlers.