I will tell you 2 overlooked Simple reasons that will be the "Kiss of Death" for a stator or regulator.
1) A battery with 1 weak cell. You must remove, charge, and load test a battery to see if it is OK.
Putting a votmeter across it tells you nothing. Going by age is risky also. If you feel the battery is getting weak due to slow cranking speed... Change it. If you don't, your charging system will have to work overtime.
2) A Poor Battery ground connector to Frame of Bike. Even a small voltage drop between the battery ground cable and Frame ground will make your stator work overtime trying to keep up with it. Of course both Battery connections must be good also.
Any votage drop across any poor connection IN THE CHARGING CIRCUIT must be made up for by the stator & regulator.
If the stator smokes because the enamel on the windings came off due to engine/oil heat, that is a different story. The enamel can just peel and chip given enough heat, time & vibration.
1 & 2 are simple "Electrical" reasons why Stators or Regulators would see an early death.