There are many factors involved in why your rig is getting looser. Fiberglass
is a plastic and will stretch and creep over time, so the boat will change shape some over time and load. Additionally like others have said the wire rigging and its fittings can stretch some. This is all normal and does not necessarily indicate any problems. If you have gone 6 years without some adjustment I would think it high time to do some tuning. I recommend this be done at least once a year depending on your sailing style. The harder you sail the more often you should do this. Another good reason for tuning is this it gives you a chance to inspect your rigging with all the covers and tape off. Inspecting is easy to do as you adjust things. Just take the time to closely look at all the fittings and connections. Look for pulled chain plates elongated holes, worn pins, and cracked fittings. If really ambitious your can also take this time to go aloft and check things. It is important to inspect things on a regular basis, just take this time now to check things out. This way you will know for sure what is going on and can either fix it or know that everything is ok and sleep better at night and you will know your rig is well tuned to boot.