It could be that the lens in your player is getting dusty.
You might try getting a can of pressurized air to gently blow into the player compartment.
Alternatively, you might consider getting a Blu-ray player cleaning disc. Do not get a DVD cleaning disc. The optics in a BD player are closer to the disk than the optics in a DVD player and can be damaged by using the wrong type of cleaner.
Or you could consider having your player cleaned professionally.