It is an unfortunate reality that many privately owned aircraft sit for longer than they should. It's the owner's privilege to have their property sit. From many owner's perspectives, yes, they'd like to have their aircraft fly more, but the risks of excess wear and tear, damage, or worse unreported damage is just not worth it. You rent an enthusiastic pilot your aircraft for ten hours, maybe clear a hundred or so dollars profit, but the slightest thing goes wrong, or gets damaged, and the time and cost to rectify it far exceeds the "income" from the rental - not worth it.
The eager pilot will have the best success getting to know an owner, and allowing them to build trust in you. Invest in their aircraft, either your time cleaning and waxing it, or paying for something it needs - to demonstrate your commitment to their investment. With that trust, you may get the use of the plane, and it might be even better and more free than you can imagine. It's just a challenging start....
I know it can be done, as I have had the great fortune to trusted with many aircraft in my flying past and present, but it was never a casual event, it was always built on getting to know the owner, and paying it forward with commitment to the condition of the aircraft.