my max cycle count is 1000 and my actual cont is 727. Why does it say to 'service battery' ?

Batteries are considered Consumable Products. Over time it will degrade to a point where it needs to be replaced. The usage is normal as the capacity will go up and down all the time and never stay always at 100%. Apple Batteries are rated for 1000 Full Battery Cycles and / or 80% Capacity before needing Evaluation or replacement.

For additional reading on Battery and Apple Computers this link may help. About battery health management in Mac notebooks and especially for the M1 and Big Sur If battery charging is paused or on hold on your Mac

While the batteries may be "rated" for a cycle you t of 1000,

there are a whole variety of usage and environmental factors

that can decrease or extent that number, with heat being one

of the larger factors.

Also, like anything else with a "lifetime use" assigned to it, some

things will fail sooner some will last longer. It is just the way

things are.