Motorcycle brakes can degrade over time and can result in brake fluid leakage or degraded effectiveness. Dust can build up around pistons preventing them to retract causing the brake pad to constantly drag against the disc. Piston seals also lose flexibility and become stiff, even come out of their place and deform resulting in loss of their designed purpose of providing seal and smooth piston movement.
Best to also change the brake pads at the same and the maintenance requires to replace brake fluid. The operation is not costly, but requires one to have basic mechanical skills, new piston seals, (dot4) brake fluid and a socket set. The example photos show a Suzuki factory fitted two piston front Tokico brake caliper, smaller engine motorcycles and rear brakes are likely to have a smaller, one piston caliper. The hardest part is taking the pistons out as they are hard to grab and easy to damage, the key is NOT TO disconnect the brake fluid hose until step #7.